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Probability

In science, the probability of an event is a number that indicates how likely the event is to occur. It is expressed as a number in the range from 0 and 1, or, using percentage notation, in the range from 0% to 100%. The more likely it is that the event will occur, the higher its probability. The probability of an impossible event is 0; that of an event that is certain to occur is 1.[note 1][1][2] The probabilities of two complementary events A and B – either A occurs or B occurs – add up to 1. A simple example is the tossing of a fair (unbiased) coin. If a coin is fair, the two possible outcomes ("heads" and "tails") are equally likely; since these two outcomes are complementary and the probability of "heads" equals the probability of "tails", the probability of each of the two outcomes equals 1/2 (which could also be written as 0.5 or 50%).

The probabilities of rolling several numbers using two dice.

These concepts have been given an axiomatic mathematical formalization in probability theory, a branch of mathematics that is used in areas of study such as statistics, mathematics, science, finance, gambling, artificial intelligence, machine learning, computer science and game theory to, for example, draw inferences about the expected frequency of events. Probability theory is also used to describe the underlying mechanics and regularities of complex systems.[3]

Interpretations

When dealing with experiments that are random and well-defined in a purely theoretical setting (like tossing a coin), probabilities can be numerically described by the number of desired outcomes, divided by the total number of all outcomes. For example, tossing a coin twice will yield "head-head", "head-tail", "tail-head", and "tail-tail" outcomes. The probability of getting an outcome of "head-head" is 1 out of 4 outcomes, or, in numerical terms, 1/4, 0.25 or 25%. However, when it comes to practical application, there are two major competing categories of probability interpretations, whose adherents hold different views about the fundamental nature of probability:

  • Objectivists assign numbers to describe some objective or physical state of affairs. The most popular version of objective probability is frequentist probability, which claims that the probability of a random event denotes the relative frequency of occurrence of an experiment's outcome when the experiment is repeated indefinitely. This interpretation considers probability to be the relative frequency "in the long run" of outcomes.[4] A modification of this is propensity probability, which interprets probability as the tendency of some experiment to yield a certain outcome, even if it is performed only once.
  • Subjectivists assign numbers per subjective probability, that is, as a degree of belief.[5] The degree of belief has been interpreted as "the price at which you would buy or sell a bet that pays 1 unit of utility if E, 0 if not E",[6] although that interpretation is not universally agreed upon.[7] The most popular version of subjective probability is Bayesian probability, which includes expert knowledge as well as experimental data to produce probabilities. The expert knowledge is represented by some (subjective) prior probability distribution. These data are incorporated in a likelihood function. The product of the prior and the likelihood, when normalized, results in a posterior probability distribution that incorporates all the information known to date.[8] By Aumann's agreement theorem, Bayesian agents whose prior beliefs are similar will end up with similar posterior beliefs. However, sufficiently different priors can lead to different conclusions, regardless of how much information the agents share.[9]

Etymology

The word probability derives from the Latin probabilitas, which can also mean "probity", a measure of the authority of a witness in a legal case in Europe, and often correlated with the witness's nobility. In a sense, this differs much from the modern meaning of probability, which in contrast is a measure of the weight of empirical evidence, and is arrived at from inductive reasoning and statistical inference.[10]

History

The scientific study of probability is a modern development of mathematics. Gambling shows that there has been an interest in quantifying the ideas of probability for millennia, but exact mathematical descriptions arose much later. There are reasons for the slow development of the mathematics of probability. Whereas games of chance provided the impetus for the mathematical study of probability, fundamental issues [note 2] are still obscured by the superstitions of gamblers.[11]

According to Richard Jeffrey, "Before the middle of the seventeenth century, the term 'probable' (Latin probabilis) meant approvable, and was applied in that sense, univocally, to opinion and to action. A probable action or opinion was one such as sensible people would undertake or hold, in the circumstances."[12] However, in legal contexts especially, 'probable' could also apply to propositions for which there was good evidence.[13]

 
Gerolamo Cardano (16th century)
 
Christiaan Huygens published one of the first books on probability (17th century)

The sixteenth-century Italian polymath Gerolamo Cardano demonstrated the efficacy of defining odds as the ratio of favourable to unfavourable outcomes (which implies that the probability of an event is given by the ratio of favourable outcomes to the total number of possible outcomes[14]). Aside from the elementary work by Cardano, the doctrine of probabilities dates to the correspondence of Pierre de Fermat and Blaise Pascal (1654). Christiaan Huygens (1657) gave the earliest known scientific treatment of the subject.[15] Jakob Bernoulli's Ars Conjectandi (posthumous, 1713) and Abraham de Moivre's Doctrine of Chances (1718) treated the subject as a branch of mathematics.[16] See Ian Hacking's The Emergence of Probability[10] and James Franklin's The Science of Conjecture[17] for histories of the early development of the very concept of mathematical probability.

The theory of errors may be traced back to Roger Cotes's Opera Miscellanea (posthumous, 1722), but a memoir prepared by Thomas Simpson in 1755 (printed 1756) first applied the theory to the discussion of errors of observation.[18] The reprint (1757) of this memoir lays down the axioms that positive and negative errors are equally probable, and that certain assignable limits define the range of all errors. Simpson also discusses continuous errors and describes a probability curve.

The first two laws of error that were proposed both originated with Pierre-Simon Laplace. The first law was published in 1774, and stated that the frequency of an error could be expressed as an exponential function of the numerical magnitude of the error—disregarding sign. The second law of error was proposed in 1778 by Laplace, and stated that the frequency of the error is an exponential function of the square of the error.[19] The second law of error is called the normal distribution or the Gauss law. "It is difficult historically to attribute that law to Gauss, who in spite of his well-known precocity had probably not made this discovery before he was two years old."[19]

Daniel Bernoulli (1778) introduced the principle of the maximum product of the probabilities of a system of concurrent errors.

 
Carl Friedrich Gauss

Adrien-Marie Legendre (1805) developed the method of least squares, and introduced it in his Nouvelles méthodes pour la détermination des orbites des comètes (New Methods for Determining the Orbits of Comets).[20] In ignorance of Legendre's contribution, an Irish-American writer, Robert Adrain, editor of "The Analyst" (1808), first deduced the law of facility of error,

 

where   is a constant depending on precision of observation, and   is a scale factor ensuring that the area under the curve equals 1. He gave two proofs, the second being essentially the same as John Herschel's (1850).[citation needed] Gauss gave the first proof that seems to have been known in Europe (the third after Adrain's) in 1809. Further proofs were given by Laplace (1810, 1812), Gauss (1823), James Ivory (1825, 1826), Hagen (1837), Friedrich Bessel (1838), W.F. Donkin (1844, 1856), and Morgan Crofton (1870). Other contributors were Ellis (1844), De Morgan (1864), Glaisher (1872), and Giovanni Schiaparelli (1875). Peters's (1856) formula[clarification needed] for r, the probable error of a single observation, is well known.

In the nineteenth century, authors on the general theory included Laplace, Sylvestre Lacroix (1816), Littrow (1833), Adolphe Quetelet (1853), Richard Dedekind (1860), Helmert (1872), Hermann Laurent (1873), Liagre, Didion and Karl Pearson. Augustus De Morgan and George Boole improved the exposition of the theory.

In 1906, Andrey Markov introduced[21] the notion of Markov chains, which played an important role in stochastic processes theory and its applications. The modern theory of probability based on the measure theory was developed by Andrey Kolmogorov in 1931.[22]

On the geometric side, contributors to The Educational Times included Miller, Crofton, McColl, Wolstenholme, Watson, and Artemas Martin.[23] See integral geometry for more information.

Theory

Like other theories, the theory of probability is a representation of its concepts in formal terms—that is, in terms that can be considered separately from their meaning. These formal terms are manipulated by the rules of mathematics and logic, and any results are interpreted or translated back into the problem domain.

There have been at least two successful attempts to formalize probability, namely the Kolmogorov formulation and the Cox formulation. In Kolmogorov's formulation (see also probability space), sets are interpreted as events and probability as a measure on a class of sets. In Cox's theorem, probability is taken as a primitive (i.e., not further analyzed), and the emphasis is on constructing a consistent assignment of probability values to propositions. In both cases, the laws of probability are the same, except for technical details.

There are other methods for quantifying uncertainty, such as the Dempster–Shafer theory or possibility theory, but those are essentially different and not compatible with the usually-understood laws of probability.

Applications

Probability theory is applied in everyday life in risk assessment and modeling. The insurance industry and markets use actuarial science to determine pricing and make trading decisions. Governments apply probabilistic methods in environmental regulation, entitlement analysis, and financial regulation.

An example of the use of probability theory in equity trading is the effect of the perceived probability of any widespread Middle East conflict on oil prices, which have ripple effects in the economy as a whole. An assessment by a commodity trader that a war is more likely can send that commodity's prices up or down, and signals other traders of that opinion. Accordingly, the probabilities are neither assessed independently nor necessarily rationally. The theory of behavioral finance emerged to describe the effect of such groupthink on pricing, on policy, and on peace and conflict.[24]

In addition to financial assessment, probability can be used to analyze trends in biology (e.g., disease spread) as well as ecology (e.g., biological Punnett squares). As with finance, risk assessment can be used as a statistical tool to calculate the likelihood of undesirable events occurring, and can assist with implementing protocols to avoid encountering such circumstances. Probability is used to design games of chance so that casinos can make a guaranteed profit, yet provide payouts to players that are frequent enough to encourage continued play.[25]

Another significant application of probability theory in everyday life is reliability. Many consumer products, such as automobiles and consumer electronics, use reliability theory in product design to reduce the probability of failure. Failure probability may influence a manufacturer's decisions on a product's warranty.[26]

The cache language model and other statistical language models that are used in natural language processing are also examples of applications of probability theory.

Mathematical treatment

 
Calculation of probability (risk) vs odds

Consider an experiment that can produce a number of results. The collection of all possible results is called the sample space of the experiment, sometimes denoted as  . The power set of the sample space is formed by considering all different collections of possible results. For example, rolling a die can produce six possible results. One collection of possible results gives an odd number on the die. Thus, the subset {1,3,5} is an element of the power set of the sample space of dice rolls. These collections are called "events". In this case, {1,3,5} is the event that the die falls on some odd number. If the results that actually occur fall in a given event, the event is said to have occurred.

A probability is a way of assigning every event a value between zero and one, with the requirement that the event made up of all possible results (in our example, the event {1,2,3,4,5,6}) is assigned a value of one. To qualify as a probability, the assignment of values must satisfy the requirement that for any collection of mutually exclusive events (events with no common results, such as the events {1,6}, {3}, and {2,4}), the probability that at least one of the events will occur is given by the sum of the probabilities of all the individual events.[27]

The probability of an event A is written as  ,[28]  , or  .[29] This mathematical definition of probability can extend to infinite sample spaces, and even uncountable sample spaces, using the concept of a measure.

The opposite or complement of an event A is the event [not A] (that is, the event of A not occurring), often denoted as  ,  , or  ; its probability is given by P(not A) = 1 − P(A).[30] As an example, the chance of not rolling a six on a six-sided die is 1 – (chance of rolling a six) = 1 − 1/6 = 5/6. For a more comprehensive treatment, see Complementary event.

If two events A and B occur on a single performance of an experiment, this is called the intersection or joint probability of A and B, denoted as  

Independent events

If two events, A and B are independent then the joint probability is[28]

 

For example, if two coins are flipped, then the chance of both being heads is  [31]

Mutually exclusive events

If either event A or event B can occur but never both simultaneously, then they are called mutually exclusive events.

If two events are mutually exclusive, then the probability of both occurring is denoted as   and

 
If two events are mutually exclusive, then the probability of either occurring is denoted as   and
 
For example, the chance of rolling a 1 or 2 on a six-sided die is  

Not mutually exclusive events

If the events are not mutually exclusive then

 
For example, when drawing a card from a deck of cards, the chance of getting a heart or a face card (J,Q,K) (or both) is   since among the 52 cards of a deck, 13 are hearts, 12 are face cards, and 3 are both: here the possibilities included in the "3 that are both" are included in each of the "13 hearts" and the "12 face cards", but should only be counted once.

Conditional probability

Conditional probability is the probability of some event A, given the occurrence of some other event B. Conditional probability is written  , and is read "the probability of A, given B". It is defined by[32]

 
If   then   is formally undefined by this expression. In this case   and   are independent, since   However, it is possible to define a conditional probability for some zero-probability events using a σ-algebra of such events (such as those arising from a continuous random variable).[33]

For example, in a bag of 2 red balls and 2 blue balls (4 balls in total), the probability of taking a red ball is   however, when taking a second ball, the probability of it being either a red ball or a blue ball depends on the ball previously taken. For example, if a red ball was taken, then the probability of picking a red ball again would be   since only 1 red and 2 blue balls would have been remaining. And if a blue ball was taken previously, the probability of taking a red ball will be  

Inverse probability

In probability theory and applications, Bayes' rule relates the odds of event   to event   before (prior to) and after (posterior to) conditioning on another event   The odds on   to event   is simply the ratio of the probabilities of the two events. When arbitrarily many events   are of interest, not just two, the rule can be rephrased as posterior is proportional to prior times likelihood,   where the proportionality symbol means that the left hand side is proportional to (i.e., equals a constant times) the right hand side as   varies, for fixed or given   (Lee, 2012; Bertsch McGrayne, 2012). In this form it goes back to Laplace (1774) and to Cournot (1843); see Fienberg (2005). See Inverse probability and Bayes' rule.

Summary of probabilities

Summary of probabilities
Event Probability
A  
not A  
A or B  
A and B  
A given B  

Relation to randomness and probability in quantum mechanics

In a deterministic universe, based on Newtonian concepts, there would be no probability if all conditions were known (Laplace's demon) (but there are situations in which sensitivity to initial conditions exceeds our ability to measure them, i.e. know them). In the case of a roulette wheel, if the force of the hand and the period of that force are known, the number on which the ball will stop would be a certainty (though as a practical matter, this would likely be true only of a roulette wheel that had not been exactly levelled – as Thomas A. Bass' Newtonian Casino revealed). This also assumes knowledge of inertia and friction of the wheel, weight, smoothness, and roundness of the ball, variations in hand speed during the turning, and so forth. A probabilistic description can thus be more useful than Newtonian mechanics for analyzing the pattern of outcomes of repeated rolls of a roulette wheel. Physicists face the same situation in the kinetic theory of gases, where the system, while deterministic in principle, is so complex (with the number of molecules typically the order of magnitude of the Avogadro constant 6.02×1023) that only a statistical description of its properties is feasible.

Probability theory is required to describe quantum phenomena.[34] A revolutionary discovery of early 20th century physics was the random character of all physical processes that occur at sub-atomic scales and are governed by the laws of quantum mechanics. The objective wave function evolves deterministically but, according to the Copenhagen interpretation, it deals with probabilities of observing, the outcome being explained by a wave function collapse when an observation is made. However, the loss of determinism for the sake of instrumentalism did not meet with universal approval. Albert Einstein famously remarked in a letter to Max Born: "I am convinced that God does not play dice".[35] Like Einstein, Erwin Schrödinger, who discovered the wave function, believed quantum mechanics is a statistical approximation of an underlying deterministic reality.[36] In some modern interpretations of the statistical mechanics of measurement, quantum decoherence is invoked to account for the appearance of subjectively probabilistic experimental outcomes.

See also

In law

Notes

  1. ^ The converse is not necessarily true. Strictly speaking, a probability of 0 indicates that an event almost never takes place, whereas a probability of 1 indicates than an event almost certainly takes place. This is an important distinction when the sample space is infinite. For example, for the continuous uniform distribution on the real interval [5, 10], there are an infinite number of possible outcomes, and the probability of any given outcome being observed — for instance, exactly 7 — is 0. This means that when we make an observation, it will almost surely not be exactly 7. However, it does not mean that exactly 7 is impossible. Ultimately some specific outcome (with probability 0) will be observed, and one possibility for that specific outcome is exactly 7.
  2. ^ In the context of the book that this is quoted from, it is the theory of probability and the logic behind it that governs the phenomena of such things compared to rash predictions that rely on pure luck or mythological arguments such as gods of luck helping the winner of the game.

References

  1. ^ "Kendall's Advanced Theory of Statistics, Volume 1: Distribution Theory", Alan Stuart and Keith Ord, 6th Ed, (2009), ISBN 978-0-534-24312-8.
  2. ^ William Feller, An Introduction to Probability Theory and Its Applications, (Vol 1), 3rd Ed, (1968), Wiley, ISBN 0-471-25708-7.
  3. ^ Probability Theory The Britannica website
  4. ^ Hacking, Ian (1965). The Logic of Statistical Inference. Cambridge University Press. ISBN 978-0-521-05165-1.[page needed]
  5. ^ Finetti, Bruno de (1970). "Logical foundations and measurement of subjective probability". Acta Psychologica. 34: 129–145. doi:10.1016/0001-6918(70)90012-0.
  6. ^ Hájek, Alan (21 October 2002). Edward N. Zalta (ed.). "Interpretations of Probability". The Stanford Encyclopedia of Philosophy (Winter 2012 ed.). Retrieved 22 April 2013.
  7. ^ Jaynes, E.T. (2003). "Section A.2 The de Finetti system of probability". In Bretthorst, G. Larry (ed.). Probability Theory: The Logic of Science (1 ed.). Cambridge University Press. ISBN 978-0-521-59271-0.
  8. ^ Hogg, Robert V.; Craig, Allen; McKean, Joseph W. (2004). Introduction to Mathematical Statistics (6th ed.). Upper Saddle River: Pearson. ISBN 978-0-13-008507-8.[page needed]
  9. ^ Jaynes, E.T. (2003). "Section 5.3 Converging and diverging views". In Bretthorst, G. Larry (ed.). Probability Theory: The Logic of Science (1 ed.). Cambridge University Press. ISBN 978-0-521-59271-0.
  10. ^ a b Hacking, I. (2006) The Emergence of Probability: A Philosophical Study of Early Ideas about Probability, Induction and Statistical Inference, Cambridge University Press, ISBN 978-0-521-68557-3[page needed]
  11. ^ Freund, John. (1973) Introduction to Probability. Dickenson ISBN 978-0-8221-0078-2 (p. 1)
  12. ^ Jeffrey, R.C., Probability and the Art of Judgment, Cambridge University Press. (1992). pp. 54–55 . ISBN 0-521-39459-7
  13. ^ Franklin, J. (2001) The Science of Conjecture: Evidence and Probability Before Pascal, Johns Hopkins University Press. (pp. 22, 113, 127)
  14. ^ "Some laws and problems in classical probability and how Cardano anticipated them Gorrochum, P. Chance magazine 2012" (PDF).
  15. ^ Abrams, William, A Brief History of Probability, Second Moment, retrieved 23 May 2008
  16. ^ Ivancevic, Vladimir G.; Ivancevic, Tijana T. (2008). Quantum leap : from Dirac and Feynman, across the universe, to human body and mind. Singapore ; Hackensack, NJ: World Scientific. p. 16. ISBN 978-981-281-927-7.
  17. ^ Franklin, James (2001). The Science of Conjecture: Evidence and Probability Before Pascal. Johns Hopkins University Press. ISBN 978-0-8018-6569-5.
  18. ^ Shoesmith, Eddie (November 1985). "Thomas Simpson and the arithmetic mean". Historia Mathematica. 12 (4): 352–355. doi:10.1016/0315-0860(85)90044-8.
  19. ^ a b Wilson EB (1923) "First and second laws of error". Journal of the American Statistical Association, 18, 143
  20. ^ Seneta, Eugene William. . StatProb: The Encyclopedia Sponsored by Statistics and Probability Societies. Archived from the original on 3 February 2016. Retrieved 27 January 2016.
  21. ^ Weber, Richard. "Markov Chains" (PDF). Statistical Laboratory. University of Cambridge.
  22. ^ Vitanyi, Paul M.B. (1988). "Andrei Nikolaevich Kolmogorov". CWI Quarterly (1): 3–18. Retrieved 27 January 2016.
  23. ^ Wilcox, Rand R. (10 May 2016). Understanding and applying basic statistical methods using R. Hoboken, New Jersey. ISBN 978-1-119-06140-3. OCLC 949759319.
  24. ^ Singh, Laurie (2010) "Whither Efficient Markets? Efficient Market Theory and Behavioral Finance". The Finance Professionals' Post, 2010.
  25. ^ Gao, J.Z.; Fong, D.; Liu, X. (April 2011). "Mathematical analyses of casino rebate systems for VIP gambling". International Gambling Studies. 11 (1): 93–106. doi:10.1080/14459795.2011.552575. S2CID 144540412.
  26. ^ Gorman, Michael F. (2010). "Management Insights". Management Science. 56: iv–vii. doi:10.1287/mnsc.1090.1132.
  27. ^ Ross, Sheldon M. (2010). A First course in Probability (8th ed.). Pearson Prentice Hall. pp. 26–27. ISBN 9780136033134.
  28. ^ a b Weisstein, Eric W. "Probability". mathworld.wolfram.com. Retrieved 10 September 2020.
  29. ^ Olofsson (2005) p. 8.
  30. ^ Olofsson (2005), p. 9
  31. ^ Olofsson (2005) p. 35.
  32. ^ Olofsson (2005) p. 29.
  33. ^ "Conditional probability with respect to a sigma-algebra". www.statlect.com. Retrieved 4 July 2022.
  34. ^ Burgin, Mark (2010). "Interpretations of Negative Probabilities". p. 1. arXiv:1008.1287v1 [physics.data-an].
  35. ^ Jedenfalls bin ich überzeugt, daß der Alte nicht würfelt. Letter to Max Born, 4 December 1926, in: Einstein/Born Briefwechsel 1916–1955.
  36. ^ Moore, W.J. (1992). Schrödinger: Life and Thought. Cambridge University Press. p. 479. ISBN 978-0-521-43767-7.

Bibliography

  • Kallenberg, O. (2005) Probabilistic Symmetries and Invariance Principles. Springer-Verlag, New York. 510 pp. ISBN 0-387-25115-4
  • Kallenberg, O. (2002) Foundations of Modern Probability, 2nd ed. Springer Series in Statistics. 650 pp. ISBN 0-387-95313-2
  • Olofsson, Peter (2005) Probability, Statistics, and Stochastic Processes, Wiley-Interscience. 504 pp ISBN 0-471-67969-0.

External links

  • Virtual Laboratories in Probability and Statistics (Univ. of Ala.-Huntsville)
  • Probability on In Our Time at the BBC
  • Probability and Statistics EBook
  • Edwin Thompson Jaynes. Probability Theory: The Logic of Science. Preprint: Washington University, (1996). — and PDF (first three chapters)
  • People from the History of Probability and Statistics (Univ. of Southampton)
  • Probability and Statistics on the Earliest Uses Pages (Univ. of Southampton)
  • Earliest Uses of Symbols in Probability and Statistics on Earliest Uses of Various Mathematical Symbols
  • A tutorial on probability and Bayes' theorem devised for first-year Oxford University students
  • [1] pdf file of An Anthology of Chance Operations (1963) at UbuWeb
  • Introduction to Probability – eBook 27 July 2011 at the Wayback Machine, by Charles Grinstead, Laurie Snell Source 25 March 2012 at the Wayback Machine (GNU Free Documentation License)
  • (in English and Italian) Bruno de Finetti, Probabilità e induzione, Bologna, CLUEB, 1993. ISBN 88-8091-176-7 (digital version)
  • Richard Feynman's Lecture on probability.

probability, mathematical, field, probability, specifically, theory, other, uses, disambiguation, science, probability, event, number, that, indicates, likely, event, occur, expressed, number, range, from, using, percentage, notation, range, from, more, likely. For the mathematical field of probability specifically see Probability theory For other uses see Probability disambiguation In science the probability of an event is a number that indicates how likely the event is to occur It is expressed as a number in the range from 0 and 1 or using percentage notation in the range from 0 to 100 The more likely it is that the event will occur the higher its probability The probability of an impossible event is 0 that of an event that is certain to occur is 1 note 1 1 2 The probabilities of two complementary events A and B either A occurs or B occurs add up to 1 A simple example is the tossing of a fair unbiased coin If a coin is fair the two possible outcomes heads and tails are equally likely since these two outcomes are complementary and the probability of heads equals the probability of tails the probability of each of the two outcomes equals 1 2 which could also be written as 0 5 or 50 The probabilities of rolling several numbers using two dice These concepts have been given an axiomatic mathematical formalization in probability theory a branch of mathematics that is used in areas of study such as statistics mathematics science finance gambling artificial intelligence machine learning computer science and game theory to for example draw inferences about the expected frequency of events Probability theory is also used to describe the underlying mechanics and regularities of complex systems 3 Contents 1 Interpretations 2 Etymology 3 History 4 Theory 5 Applications 6 Mathematical treatment 6 1 Independent events 6 2 Mutually exclusive events 6 3 Not mutually exclusive events 6 4 Conditional probability 6 5 Inverse probability 6 6 Summary of probabilities 7 Relation to randomness and probability in quantum mechanics 8 See also 9 Notes 10 References 11 Bibliography 12 External linksInterpretations EditMain article Probability interpretations When dealing with experiments that are random and well defined in a purely theoretical setting like tossing a coin probabilities can be numerically described by the number of desired outcomes divided by the total number of all outcomes For example tossing a coin twice will yield head head head tail tail head and tail tail outcomes The probability of getting an outcome of head head is 1 out of 4 outcomes or in numerical terms 1 4 0 25 or 25 However when it comes to practical application there are two major competing categories of probability interpretations whose adherents hold different views about the fundamental nature of probability Objectivists assign numbers to describe some objective or physical state of affairs The most popular version of objective probability is frequentist probability which claims that the probability of a random event denotes the relative frequency of occurrence of an experiment s outcome when the experiment is repeated indefinitely This interpretation considers probability to be the relative frequency in the long run of outcomes 4 A modification of this is propensity probability which interprets probability as the tendency of some experiment to yield a certain outcome even if it is performed only once Subjectivists assign numbers per subjective probability that is as a degree of belief 5 The degree of belief has been interpreted as the price at which you would buy or sell a bet that pays 1 unit of utility if E 0 if not E 6 although that interpretation is not universally agreed upon 7 The most popular version of subjective probability is Bayesian probability which includes expert knowledge as well as experimental data to produce probabilities The expert knowledge is represented by some subjective prior probability distribution These data are incorporated in a likelihood function The product of the prior and the likelihood when normalized results in a posterior probability distribution that incorporates all the information known to date 8 By Aumann s agreement theorem Bayesian agents whose prior beliefs are similar will end up with similar posterior beliefs However sufficiently different priors can lead to different conclusions regardless of how much information the agents share 9 Etymology EditSee also History of probability Etymology and Glossary of probability and statistics Further information Likelihood The word probability derives from the Latin probabilitas code lat promoted to code la which can also mean probity a measure of the authority of a witness in a legal case in Europe and often correlated with the witness s nobility In a sense this differs much from the modern meaning of probability which in contrast is a measure of the weight of empirical evidence and is arrived at from inductive reasoning and statistical inference 10 History EditMain article History of probability Further information History of statistics The scientific study of probability is a modern development of mathematics Gambling shows that there has been an interest in quantifying the ideas of probability for millennia but exact mathematical descriptions arose much later There are reasons for the slow development of the mathematics of probability Whereas games of chance provided the impetus for the mathematical study of probability fundamental issues note 2 are still obscured by the superstitions of gamblers 11 According to Richard Jeffrey Before the middle of the seventeenth century the term probable Latin probabilis meant approvable and was applied in that sense univocally to opinion and to action A probable action or opinion was one such as sensible people would undertake or hold in the circumstances 12 However in legal contexts especially probable could also apply to propositions for which there was good evidence 13 Gerolamo Cardano 16th century Christiaan Huygens published one of the first books on probability 17th century The sixteenth century Italian polymath Gerolamo Cardano demonstrated the efficacy of defining odds as the ratio of favourable to unfavourable outcomes which implies that the probability of an event is given by the ratio of favourable outcomes to the total number of possible outcomes 14 Aside from the elementary work by Cardano the doctrine of probabilities dates to the correspondence of Pierre de Fermat and Blaise Pascal 1654 Christiaan Huygens 1657 gave the earliest known scientific treatment of the subject 15 Jakob Bernoulli s Ars Conjectandi posthumous 1713 and Abraham de Moivre s Doctrine of Chances 1718 treated the subject as a branch of mathematics 16 See Ian Hacking s The Emergence of Probability 10 and James Franklin s The Science of Conjecture 17 for histories of the early development of the very concept of mathematical probability The theory of errors may be traced back to Roger Cotes s Opera Miscellanea posthumous 1722 but a memoir prepared by Thomas Simpson in 1755 printed 1756 first applied the theory to the discussion of errors of observation 18 The reprint 1757 of this memoir lays down the axioms that positive and negative errors are equally probable and that certain assignable limits define the range of all errors Simpson also discusses continuous errors and describes a probability curve The first two laws of error that were proposed both originated with Pierre Simon Laplace The first law was published in 1774 and stated that the frequency of an error could be expressed as an exponential function of the numerical magnitude of the error disregarding sign The second law of error was proposed in 1778 by Laplace and stated that the frequency of the error is an exponential function of the square of the error 19 The second law of error is called the normal distribution or the Gauss law It is difficult historically to attribute that law to Gauss who in spite of his well known precocity had probably not made this discovery before he was two years old 19 Daniel Bernoulli 1778 introduced the principle of the maximum product of the probabilities of a system of concurrent errors Carl Friedrich Gauss Adrien Marie Legendre 1805 developed the method of least squares and introduced it in his Nouvelles methodes pour la determination des orbites des cometes New Methods for Determining the Orbits of Comets 20 In ignorance of Legendre s contribution an Irish American writer Robert Adrain editor of The Analyst 1808 first deduced the law of facility of error ϕ x c e h 2 x 2 displaystyle phi x ce h 2 x 2 where h displaystyle h is a constant depending on precision of observation and c displaystyle c is a scale factor ensuring that the area under the curve equals 1 He gave two proofs the second being essentially the same as John Herschel s 1850 citation needed Gauss gave the first proof that seems to have been known in Europe the third after Adrain s in 1809 Further proofs were given by Laplace 1810 1812 Gauss 1823 James Ivory 1825 1826 Hagen 1837 Friedrich Bessel 1838 W F Donkin 1844 1856 and Morgan Crofton 1870 Other contributors were Ellis 1844 De Morgan 1864 Glaisher 1872 and Giovanni Schiaparelli 1875 Peters s 1856 formula clarification needed for r the probable error of a single observation is well known In the nineteenth century authors on the general theory included Laplace Sylvestre Lacroix 1816 Littrow 1833 Adolphe Quetelet 1853 Richard Dedekind 1860 Helmert 1872 Hermann Laurent 1873 Liagre Didion and Karl Pearson Augustus De Morgan and George Boole improved the exposition of the theory In 1906 Andrey Markov introduced 21 the notion of Markov chains which played an important role in stochastic processes theory and its applications The modern theory of probability based on the measure theory was developed by Andrey Kolmogorov in 1931 22 On the geometric side contributors to The Educational Times included Miller Crofton McColl Wolstenholme Watson and Artemas Martin 23 See integral geometry for more information Theory EditMain article Probability theory Like other theories the theory of probability is a representation of its concepts in formal terms that is in terms that can be considered separately from their meaning These formal terms are manipulated by the rules of mathematics and logic and any results are interpreted or translated back into the problem domain There have been at least two successful attempts to formalize probability namely the Kolmogorov formulation and the Cox formulation In Kolmogorov s formulation see also probability space sets are interpreted as events and probability as a measure on a class of sets In Cox s theorem probability is taken as a primitive i e not further analyzed and the emphasis is on constructing a consistent assignment of probability values to propositions In both cases the laws of probability are the same except for technical details There are other methods for quantifying uncertainty such as the Dempster Shafer theory or possibility theory but those are essentially different and not compatible with the usually understood laws of probability Applications EditProbability theory is applied in everyday life in risk assessment and modeling The insurance industry and markets use actuarial science to determine pricing and make trading decisions Governments apply probabilistic methods in environmental regulation entitlement analysis and financial regulation An example of the use of probability theory in equity trading is the effect of the perceived probability of any widespread Middle East conflict on oil prices which have ripple effects in the economy as a whole An assessment by a commodity trader that a war is more likely can send that commodity s prices up or down and signals other traders of that opinion Accordingly the probabilities are neither assessed independently nor necessarily rationally The theory of behavioral finance emerged to describe the effect of such groupthink on pricing on policy and on peace and conflict 24 In addition to financial assessment probability can be used to analyze trends in biology e g disease spread as well as ecology e g biological Punnett squares As with finance risk assessment can be used as a statistical tool to calculate the likelihood of undesirable events occurring and can assist with implementing protocols to avoid encountering such circumstances Probability is used to design games of chance so that casinos can make a guaranteed profit yet provide payouts to players that are frequent enough to encourage continued play 25 Another significant application of probability theory in everyday life is reliability Many consumer products such as automobiles and consumer electronics use reliability theory in product design to reduce the probability of failure Failure probability may influence a manufacturer s decisions on a product s warranty 26 The cache language model and other statistical language models that are used in natural language processing are also examples of applications of probability theory Mathematical treatment Edit Calculation of probability risk vs odds See also Probability axioms Consider an experiment that can produce a number of results The collection of all possible results is called the sample space of the experiment sometimes denoted as W displaystyle Omega The power set of the sample space is formed by considering all different collections of possible results For example rolling a die can produce six possible results One collection of possible results gives an odd number on the die Thus the subset 1 3 5 is an element of the power set of the sample space of dice rolls These collections are called events In this case 1 3 5 is the event that the die falls on some odd number If the results that actually occur fall in a given event the event is said to have occurred A probability is a way of assigning every event a value between zero and one with the requirement that the event made up of all possible results in our example the event 1 2 3 4 5 6 is assigned a value of one To qualify as a probability the assignment of values must satisfy the requirement that for any collection of mutually exclusive events events with no common results such as the events 1 6 3 and 2 4 the probability that at least one of the events will occur is given by the sum of the probabilities of all the individual events 27 The probability of an event A is written as P A displaystyle P A 28 p A displaystyle p A or Pr A displaystyle text Pr A 29 This mathematical definition of probability can extend to infinite sample spaces and even uncountable sample spaces using the concept of a measure The opposite or complement of an event A is the event not A that is the event of A not occurring often denoted as A A c displaystyle A A c A A A displaystyle overline A A complement neg A or A displaystyle sim A its probability is given by P not A 1 P A 30 As an example the chance of not rolling a six on a six sided die is 1 chance of rolling a six 1 1 6 5 6 For a more comprehensive treatment see Complementary event If two events A and B occur on a single performance of an experiment this is called the intersection or joint probability of A and B denoted as P A B displaystyle P A cap B Independent events Edit If two events A and B are independent then the joint probability is 28 P A and B P A B P A P B displaystyle P A mbox and B P A cap B P A P B For example if two coins are flipped then the chance of both being heads is 1 2 1 2 1 4 displaystyle tfrac 1 2 times tfrac 1 2 tfrac 1 4 31 Mutually exclusive events Edit Main article Mutual exclusivity If either event A or event B can occur but never both simultaneously then they are called mutually exclusive events If two events are mutually exclusive then the probability of both occurring is denoted as P A B displaystyle P A cap B andP A and B P A B 0 displaystyle P A mbox and B P A cap B 0 If two events are mutually exclusive then the probability of either occurring is denoted as P A B displaystyle P A cup B and P A or B P A B P A P B P A B P A P B 0 P A P B displaystyle P A mbox or B P A cup B P A P B P A cap B P A P B 0 P A P B For example the chance of rolling a 1 or 2 on a six sided die is P 1 or 2 P 1 P 2 1 6 1 6 1 3 displaystyle P 1 mbox or 2 P 1 P 2 tfrac 1 6 tfrac 1 6 tfrac 1 3 Not mutually exclusive events Edit If the events are not mutually exclusive thenP A or B P A B P A P B P A and B displaystyle P left A hbox or B right P A cup B P left A right P left B right P left A mbox and B right For example when drawing a card from a deck of cards the chance of getting a heart or a face card J Q K or both is 13 52 12 52 3 52 11 26 displaystyle tfrac 13 52 tfrac 12 52 tfrac 3 52 tfrac 11 26 since among the 52 cards of a deck 13 are hearts 12 are face cards and 3 are both here the possibilities included in the 3 that are both are included in each of the 13 hearts and the 12 face cards but should only be counted once Conditional probability Edit Conditional probability is the probability of some event A given the occurrence of some other event B Conditional probability is written P A B displaystyle P A mid B and is read the probability of A given B It is defined by 32 P A B P A B P B displaystyle P A mid B frac P A cap B P B If P B 0 displaystyle P B 0 then P A B displaystyle P A mid B is formally undefined by this expression In this case A displaystyle A and B displaystyle B are independent since P A B P A P B 0 displaystyle P A cap B P A P B 0 However it is possible to define a conditional probability for some zero probability events using a s algebra of such events such as those arising from a continuous random variable 33 For example in a bag of 2 red balls and 2 blue balls 4 balls in total the probability of taking a red ball is 1 2 displaystyle 1 2 however when taking a second ball the probability of it being either a red ball or a blue ball depends on the ball previously taken For example if a red ball was taken then the probability of picking a red ball again would be 1 3 displaystyle 1 3 since only 1 red and 2 blue balls would have been remaining And if a blue ball was taken previously the probability of taking a red ball will be 2 3 displaystyle 2 3 Inverse probability Edit In probability theory and applications Bayes rule relates the odds of event A 1 displaystyle A 1 to event A 2 displaystyle A 2 before prior to and after posterior to conditioning on another event B displaystyle B The odds on A 1 displaystyle A 1 to event A 2 displaystyle A 2 is simply the ratio of the probabilities of the two events When arbitrarily many events A displaystyle A are of interest not just two the rule can be rephrased as posterior is proportional to prior times likelihood P A B P A P B A displaystyle P A B propto P A P B A where the proportionality symbol means that the left hand side is proportional to i e equals a constant times the right hand side as A displaystyle A varies for fixed or given B displaystyle B Lee 2012 Bertsch McGrayne 2012 In this form it goes back to Laplace 1774 and to Cournot 1843 see Fienberg 2005 See Inverse probability and Bayes rule Summary of probabilities Edit Summary of probabilities Event ProbabilityA P A 0 1 displaystyle P A in 0 1 not A P A 1 P A displaystyle P A complement 1 P A A or B P A B P A P B P A B P A B P A P B if A and B are mutually exclusive displaystyle begin aligned P A cup B amp P A P B P A cap B P A cup B amp P A P B qquad mbox if A and B are mutually exclusive end aligned A and B P A B P A B P B P B A P A P A B P A P B if A and B are independent displaystyle begin aligned P A cap B amp P A B P B P B A P A P A cap B amp P A P B qquad mbox if A and B are independent end aligned A given B P A B P A B P B P B A P A P B displaystyle P A mid B frac P A cap B P B frac P B A P A P B Relation to randomness and probability in quantum mechanics EditMain article Randomness See also Quantum fluctuation Interpretations In a deterministic universe based on Newtonian concepts there would be no probability if all conditions were known Laplace s demon but there are situations in which sensitivity to initial conditions exceeds our ability to measure them i e know them In the case of a roulette wheel if the force of the hand and the period of that force are known the number on which the ball will stop would be a certainty though as a practical matter this would likely be true only of a roulette wheel that had not been exactly levelled as Thomas A Bass Newtonian Casino revealed This also assumes knowledge of inertia and friction of the wheel weight smoothness and roundness of the ball variations in hand speed during the turning and so forth A probabilistic description can thus be more useful than Newtonian mechanics for analyzing the pattern of outcomes of repeated rolls of a roulette wheel Physicists face the same situation in the kinetic theory of gases where the system while deterministic in principle is so complex with the number of molecules typically the order of magnitude of the Avogadro constant 6 02 1023 that only a statistical description of its properties is feasible Probability theory is required to describe quantum phenomena 34 A revolutionary discovery of early 20th century physics was the random character of all physical processes that occur at sub atomic scales and are governed by the laws of quantum mechanics The objective wave function evolves deterministically but according to the Copenhagen interpretation it deals with probabilities of observing the outcome being explained by a wave function collapse when an observation is made However the loss of determinism for the sake of instrumentalism did not meet with universal approval Albert Einstein famously remarked in a letter to Max Born I am convinced that God does not play dice 35 Like Einstein Erwin Schrodinger who discovered the wave function believed quantum mechanics is a statistical approximation of an underlying deterministic reality 36 In some modern interpretations of the statistical mechanics of measurement quantum decoherence is invoked to account for the appearance of subjectively probabilistic experimental outcomes See also Edit Mathematics portal Philosophy portalMain article Outline of probability Chance disambiguation Class membership probabilities Contingency Equiprobability Fuzzy logic Heuristics in judgment and decision making Probability theory Randomness Statistics Estimators Estimation theory Probability density estimation Probability density function Pairwise independence In lawBalance of probabilitiesNotes Edit The converse is not necessarily true Strictly speaking a probability of 0 indicates that an event almost never takes place whereas a probability of 1 indicates than an event almost certainly takes place This is an important distinction when the sample space is infinite For example for the continuous uniform distribution on the real interval 5 10 there are an infinite number of possible outcomes and the probability of any given outcome being observed for instance exactly 7 is 0 This means that when we make an observation it will almost surely not be exactly 7 However it does not mean that exactly 7 is impossible Ultimately some specific outcome with probability 0 will be observed and one possibility for that specific outcome is exactly 7 In the context of the book that this is quoted from it is the theory of probability and the logic behind it that governs the phenomena of such things compared to rash predictions that rely on pure luck or mythological arguments such as gods of luck helping the winner of the game References Edit Kendall s Advanced Theory of Statistics Volume 1 Distribution Theory Alan Stuart and Keith Ord 6th Ed 2009 ISBN 978 0 534 24312 8 William Feller An Introduction to Probability Theory and Its Applications Vol 1 3rd Ed 1968 Wiley ISBN 0 471 25708 7 Probability Theory The Britannica website Hacking Ian 1965 The Logic of Statistical Inference Cambridge University Press ISBN 978 0 521 05165 1 page needed Finetti Bruno de 1970 Logical foundations and measurement of subjective probability Acta Psychologica 34 129 145 doi 10 1016 0001 6918 70 90012 0 Hajek Alan 21 October 2002 Edward N Zalta ed Interpretations of Probability The Stanford Encyclopedia of Philosophy Winter 2012 ed Retrieved 22 April 2013 Jaynes E T 2003 Section A 2 The de Finetti system of probability In Bretthorst G Larry ed Probability Theory The Logic of Science 1 ed Cambridge University Press ISBN 978 0 521 59271 0 Hogg Robert V Craig Allen McKean Joseph W 2004 Introduction to Mathematical Statistics 6th ed Upper Saddle River Pearson ISBN 978 0 13 008507 8 page needed Jaynes E T 2003 Section 5 3 Converging and diverging views In Bretthorst G Larry ed Probability Theory The Logic of Science 1 ed Cambridge University Press ISBN 978 0 521 59271 0 a b Hacking I 2006 The Emergence of Probability A Philosophical Study of Early Ideas about Probability Induction and Statistical Inference Cambridge University Press ISBN 978 0 521 68557 3 page needed Freund John 1973 Introduction to Probability Dickenson ISBN 978 0 8221 0078 2 p 1 Jeffrey R C Probability and the Art of Judgment Cambridge University Press 1992 pp 54 55 ISBN 0 521 39459 7 Franklin J 2001 The Science of Conjecture Evidence and Probability Before Pascal Johns Hopkins University Press pp 22 113 127 Some laws and problems in classical probability and how Cardano anticipated them Gorrochum P Chance magazine 2012 PDF Abrams William A Brief History of Probability Second Moment retrieved 23 May 2008 Ivancevic Vladimir G Ivancevic Tijana T 2008 Quantum leap from Dirac and Feynman across the universe to human body and mind Singapore Hackensack NJ World Scientific p 16 ISBN 978 981 281 927 7 Franklin James 2001 The Science of Conjecture Evidence and Probability Before Pascal Johns Hopkins University Press ISBN 978 0 8018 6569 5 Shoesmith Eddie November 1985 Thomas Simpson and the arithmetic mean Historia Mathematica 12 4 352 355 doi 10 1016 0315 0860 85 90044 8 a b Wilson EB 1923 First and second laws of error Journal of the American Statistical Association 18 143 Seneta Eugene William Adrien Marie Legendre version 9 StatProb The Encyclopedia Sponsored by Statistics and Probability Societies Archived from the original on 3 February 2016 Retrieved 27 January 2016 Weber Richard Markov Chains PDF Statistical Laboratory University of Cambridge Vitanyi Paul M B 1988 Andrei Nikolaevich Kolmogorov CWI Quarterly 1 3 18 Retrieved 27 January 2016 Wilcox Rand R 10 May 2016 Understanding and applying basic statistical methods using R Hoboken New Jersey ISBN 978 1 119 06140 3 OCLC 949759319 Singh Laurie 2010 Whither Efficient Markets Efficient Market Theory and Behavioral Finance The Finance Professionals Post 2010 Gao J Z Fong D Liu X April 2011 Mathematical analyses of casino rebate systems for VIP gambling International Gambling Studies 11 1 93 106 doi 10 1080 14459795 2011 552575 S2CID 144540412 Gorman Michael F 2010 Management Insights Management Science 56 iv vii doi 10 1287 mnsc 1090 1132 Ross Sheldon M 2010 A First course in Probability 8th ed Pearson Prentice Hall pp 26 27 ISBN 9780136033134 a b Weisstein Eric W Probability mathworld wolfram com Retrieved 10 September 2020 Olofsson 2005 p 8 Olofsson 2005 p 9 Olofsson 2005 p 35 Olofsson 2005 p 29 Conditional probability with respect to a sigma algebra www statlect com Retrieved 4 July 2022 Burgin Mark 2010 Interpretations of Negative Probabilities p 1 arXiv 1008 1287v1 physics data an Jedenfalls bin ich uberzeugt dass der Alte nicht wurfelt Letter to Max Born 4 December 1926 in Einstein Born Briefwechsel 1916 1955 Moore W J 1992 Schrodinger Life and Thought Cambridge University Press p 479 ISBN 978 0 521 43767 7 Bibliography EditKallenberg O 2005 Probabilistic Symmetries and Invariance Principles Springer Verlag New York 510 pp ISBN 0 387 25115 4 Kallenberg O 2002 Foundations of Modern Probability 2nd ed Springer Series in Statistics 650 pp ISBN 0 387 95313 2 Olofsson Peter 2005 Probability Statistics and Stochastic Processes Wiley Interscience 504 pp ISBN 0 471 67969 0 External links Edit Wikiquote has quotations related to Probability Wikibooks has more on the topic of Probability Wikimedia Commons has media related to Probability Virtual Laboratories in Probability and Statistics Univ of Ala Huntsville Probability on In Our Time at the BBC Probability and Statistics EBook Edwin Thompson Jaynes Probability Theory The Logic of Science Preprint Washington University 1996 HTML index with links to PostScript files and PDF first three chapters People from the History of Probability and Statistics Univ of Southampton Probability and Statistics on the Earliest Uses Pages Univ of Southampton Earliest Uses of Symbols in Probability and Statistics on Earliest Uses of Various Mathematical Symbols A tutorial on probability and Bayes theorem devised for first year Oxford University students 1 pdf file of An Anthology of Chance Operations 1963 at UbuWeb Introduction to Probability eBook Archived 27 July 2011 at the Wayback Machine by Charles Grinstead Laurie Snell Source Archived 25 March 2012 at the Wayback Machine GNU Free Documentation License in English and Italian Bruno de Finetti Probabilita e induzione Bologna CLUEB 1993 ISBN 88 8091 176 7 digital version Richard Feynman s Lecture on probability Portal Mathematics Retrieved from https en wikipedia org w index php title Probability amp oldid 1142220765, wikipedia, wiki, book, books, library,

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