# Probability

Certainty series
This box:     [ edit]

Probability is the likelihood that something is the case or will happen. Probability theory is used extensively in areas such as statistics, mathematics, science and philosophy to draw conclusions about the likelihood of potential events and the underlying mechanics of complex systems.

## Interpretations

The word probability does not have a consistent direct definition. Actually, there are two broad categories of probability interpretations: Frequentists talk about probabilities only when dealing with well defined random experiments. The relative frequency of occurrence of an experiment's outcome, when repeating the experiment, is a measure of the probability of that random event. Bayesians, however, assign probabilities to any statement whatsoever, even when no random process is involved, as a way to represent its subjective plausibility.

## History

Further information: Statistics
The scientific study of probability is a modern development. Gambling shows that there has been an interest in quantifying the ideas of probability for millennia, but exact mathematical descriptions of use in those problems only arose much later.

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."[1]

Aside from some elementary considerations made by Girolamo Cardano in the 16th century, 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. Jakob Bernoulli's Ars Conjectandi (posthumous, 1713) and Abraham de Moivre's Doctrine of Chances (1718) treated the subject as a branch of mathematics. See Ian Hacking's The Emergence of Probability for a history 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. The reprint (1757) of this memoir lays down the axioms that positive and negative errors are equally probable, and that there are certain assignable limits within which all errors may be supposed to fall; continuous errors are discussed and a probability curve is given.

Pierre-Simon Laplace (1774) made the first attempt to deduce a rule for the combination of observations from the principles of the theory of probabilities. He represented the law of probability of errors by a curve , being any error and its probability, and laid down three properties of this curve:
1. it is symmetric as to the -axis;
2. the -axis is an asymptote, the probability of the error being 0;
3. the area enclosed is 1, it being certain that an error exists.
He deduced a formula for the mean of three observations. He also gave (1781) a formula for the law of facility of error (a term due to Lagrange, 1774), but one which led to unmanageable equations. Daniel Bernoulli (1778) introduced the principle of the maximum product of the probabilities of a system of concurrent errors.

The method of least squares is due to Adrien-Marie Legendre (1805), who introduced it in his Nouvelles méthodes pour la détermination des orbites des comètes (New Methods for Determining the Orbits of Comets). 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,

and being constants depending on precision of observation. He gave two proofs, the second being essentially the same as John Herschel's (1850). Gauss gave the first proof which 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 for , 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.

On the geometric side (see integral geometry) contributors to The Educational Times were influential (Miller, Crofton, McColl, Wolstenholme, Watson, and Artemas Martin).

## Theory

Main article: Probability theory
Like other theories, the theory of probability is a representation of probabilistic 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 then interpreted or translated back into the problem domain.

In probability theory, a probability is represented by a real number in the range from 0 to 1. An impossible event has a probability of 0, and a certain event has a probability of 1. (However, other events may also have probabilities 0 or 1: events with probability 0 are not necessarily impossible, and those with probability 1 are not necessarily certain. For examples, see Almost surely.)

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

## Applications

Two major applications of probability theory in everyday life are in risk assessment and in trade on commodity markets. Governments typically apply probabilistic methods in environmental regulation where it is called "pathway analysis", often measuring well-being using methods that are stochastic in nature, and choosing projects to undertake based on statistical analyses of their probable effect on the population as a whole. It is not correct to say that statistics are involved in the modelling itself, as typically the assessments of risk are one-time and thus require more fundamental probability models, e.g. "the probability of another 9/11". A law of small numbers tends to apply to all such choices and perception of the effect of such choices, which makes probability measures a political matter.

A good example 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 vs. less likely sends prices up or down, and signals other traders of that opinion. Accordingly, the probabilities are not assessed independently nor necessarily very rationally. The theory of behavioral finance emerged to describe the effect of such groupthink on pricing, on policy, and on peace and conflict.

It can reasonably be said that the discovery of rigorous methods to assess and combine probability assessments has had a profound effect on modern society. Accordingly, it may be of some importance to most citizens to understand how odds and probability assessments are made, and how they contribute to reputations and to decisions, especially in a democracy.

Another significant application of probability theory in everyday life is reliability. Many consumer products, such as automobiles and consumer electronics, utilize reliability theory in the design of the product in order to reduce the probability of failure. The probability of failure is also closely associated with the product's warranty.

It could be said that there is no such thing as probability. It could also be said that probability is a measure of our degree of uncertainty, or that is, the extent of our ignorance in a given situation. Consequently, there might be a probability of 1 in 52 that the top card in a deck of cards is the Jack of diamonds. However, if one looks at the top card and replaces it, then the probability is either 100% or zero percent, and the correct choice can be accurately made by the viewer. Modern physics provides important examples of deterministic situations where only probabilistic description is feasible due to incomplete information and complexity of a system as well as examples of truly random phenomena.

In a deterministic universe, based on Newtonian concepts, there is no probability if all conditions are known. In the case of a roulette wheel, if the force of the hand and the period of that force are known, then the number on which the ball will stop would be a certainty. Of course, 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 analysing the pattern of outcomes of repeated rolls of roulette wheel. Physicists face the same situation in 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 Avogadro constant ) that only statistical description of its properties is feasible.

A revolutionary discovery of 20th century physics was the random character of all physical processes that occur at microscopic scales and are governed by the laws of quantum mechanics. The wave function itself evolves deterministically as long as no observation is made, but, according to the prevailing Copenhagen interpretation, the randomness of the wave function collapse when an observation is made, is fundamental. This means that probability theory is required to describe nature. Some scientists spoke of expulsion from Paradise. Others never came to terms with the loss of determinism. Albert Einstein famously in a letter to Max Born: Jedenfalls bin ich überzeugt, daß der Alte nicht würfelt. (I am convinced that God does not play dice). Although alternative viewpoints exist, such as that of quantum decoherence being the cause of an apparent random collapse, at present there is a firm consensus among the physicists that probability theory is necessary to describe quantum phenomena.

## References

1. ^ Jeffrey, R.C., Probability and the Art of Judgment, Cambridge University Press. (1992). pp. 54-55 . ISBN 0-521-39459-7
• Olav Kallenberg, Probabilistic Symmetries and Invariance Principles. Springer -Verlag, New York (2005). 510 pp. ISBN 0-387-25115-4
• Kallenberg, O., Foundations of Modern Probability, 2nd ed. Springer Series in Statistics. (2002). 650 pp. ISBN 0-387-95313-2

## Quotations

• Damon Runyon, "It may be that the race is not always to the swift, nor the battle to the strong - but that is the way to bet."
• Pierre-Simon Laplace "It is remarkable that a science which began with the consideration of games of chance should have become the most important object of human knowledge." Théorie Analytique des Probabilités, 1812.
• Richard von Mises "The unlimited extension of the validity of the exact sciences was a characteristic feature of the exaggerated rationalism of the eighteenth century" (in reference to Laplace). Probability, Statistics, and Truth, p 9. Dover edition, 1981 (republication of second English edition, 1957).

Certainty is the state of being without doubt. Certainty is a condition of the total continuity of foundational inquiry. Something is certain only if no skepticism can occur. Philosophy (at least historically) struggles toward certainty.
Nihilism (from the Latin nihil, nothing) is a philosophical position, sometimes called an anti-philosophy, which argues that the world, especially past and current human existence, is without objective meaning, purpose, comprehensible truth, or essential value.
God

General approaches
Agnosticism Atheism
Deism Dystheism
Henotheism Ignosticism
Monism Monotheism
Natural theology Nontheism
Pandeism Panentheism
Pantheism Polytheism
Theism Theology
Transtheism

Specific conceptions
Uncertainty is a term used in subtly different ways in a number of fields, including philosophy, statistics, economics, finance, insurance, psychology, engineering and science.
An approximation is an inexact representation of something that is still close enough to be useful. Although approximation is most often applied to numbers, it is also frequently applied to such things as mathematical functions, shapes, and physical laws.
Belief is the psychological state in which an individual is convinced of the truth or validity of a proposition or premise (argument). Belief does not necessarily confer the ability to adequately prove one's main contention to other people, who may disagree.
Certainty is the state of being without doubt. Certainty is a condition of the total continuity of foundational inquiry. Something is certain only if no skepticism can occur. Philosophy (at least historically) struggles toward certainty.
Determinism is the philosophical proposition that every event, including human cognition and behavior, decision and action, is causally determined by an unbroken chain of prior occurrences.
Probability theory is the branch of mathematics concerned with analysis of random phenomena.[1] The central objects of probability theory are random variables, stochastic processes, and events: mathematical abstractions of non-deterministic events or measured quantities
Statistics is a mathematical science pertaining to the collection, analysis, interpretation or explanation, and presentation of data. It is applicable to a wide variety of academic disciplines, from the physical and social sciences to the humanities.
Mathematics (colloquially, maths or math) is the body of knowledge centered on such concepts as quantity, structure, space, and change, and also the academic discipline that studies them. Benjamin Peirce called it "the science that draws necessary conclusions".
Science (from the Latin scientia, 'knowledge'), in the broadest sense, refers to any systematic knowledge or practice.[1] Examples of the broader use included political science and computer science, which are not incorrectly named, but rather named according to
Philosophy is the discipline concerned with questions of how one should live (ethics); what sorts of things exist and what are their essential natures (metaphysics); what counts as genuine knowledge (epistemology); and what are the correct principles of reasoning (logic).
probability interpretations which can be called physical and evidential probabilities. Physical probabilities, which are also called objective or frequency probabilities, are associated with random physical systems such as roulette wheels, rolling dice and
Frequency probability is the interpretation of probability that defines an event's probability as the "limit" of its relative frequency in a large number of trials.
random is used to express lack of order, purpose, cause, or predictability in non-scientific parlance. A random process is a repeating process whose outcomes follow no describable deterministic pattern, but follow a probability distribution.
Bayesian probability is an interpretation of the probability calculus which holds that the concept of probability can be defined as the degree to which a person (or community) believes that a proposition is true.
Statistics is a mathematical science pertaining to the collection, analysis, interpretation or explanation, and presentation of data. It is applicable to a wide variety of academic disciplines, from the physical and social sciences to the humanities.
gambling has had many different meanings depending on the cultural and historical context in which it is used. Currently, in Western societies, it has an economic definition, referring to "wagering money or something of material value on an event with an uncertain outcome with the
Gerolamo Cardano or Girolamo Cardano (English Jerome Cardan, Latin Hieronymus Cardanus; September 24, 1501 - September 21 1576) was a celebrated Italian Renaissance mathematician, physician, astrologer, and gambler.
Pierre de Fermat IPA: [pjɛːʁ dəfɛʁ'ma] (August 17 1601 – January 12 1665) was a French lawyer at the Parlement
Blaise Pascal (pronounced [blɛːz paskal]), (June 19 1623 – August 19 1662) was a French mathematician, physicist, and religious philosopher. He was a child prodigy who was educated by his father.
Christiaan Huygens

Christiaan Huygens
Born March 14 1629
The Hague, Netherlands
Died July 8 1695 (aged 66)
Jacob Bernoulli

Jacob Bernoulli
Born November 27 1654
Basel, Switzerland
Died July 16 1705 (aged 52)
Abraham de Moivre (May 26, 1667 in Vitry-le-François, Champagne, France – November 27, 1754 in London, England; pronounced as /abʁam də mwavʁ/
Evidence
Part of the common law series
Types of evidence
Testimony · Documentary evidence
Physical evidence · Digital evidence
Exculpatory evidence · Scientific evidence
Ian Hacking, CC, Ph.D., FRSC, FBA (born February 18, 1936 in Vancouver) is a Canadian university professor and philosopher, specializing in the philosophy of science.
Roger Cotes

Roger Cotes (1682-1716).
Born July 10, 1682
Burbage, Leicestershire
Died June 5, 1716
Cambridge, Cambridgeshire
Residence UK
Nationality British

Thomas Simpson (August 20, 1710 – May 14, 1761) was a British mathematician, inventor and eponym of Simpson's rule to approximate definite integrals.