# Probability

- The likelihood that something will happen. For example, a probability of less than .05 indicates that the probability of something occurring by chance alone is less than 5 in 100, or 5 percent. This level of probability is usually taken as the level of biologic significance, so a higher incidence may be considered meaningful. The abbreviation for probability is P.
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**1.**A*measure*, ranging from 0 to 1, of the*likelihood*of truth of a*hypothesis*or statement.**2.**The*limit*of the relative*frequency*of an*event*in a*sequence*of N*random*trials as N approaches*infinity*.-**conditional p.**a p. quoted when the*range*of choices admitted is restricted, i.e., conditional;*thus*, the p. of the child of a color-blind man inheriting the*gene*is 1/2 if the child is*female*and almost 0 if the child is*male*.-the p. that two or more outcomes are realized jointly.*joint*p.-a p. of an outcome based either on unassailable*objective*p.*theory*or extensive*empiric**experience*of exactly the same*combination*of circumstances; the notion also implies that the realization concerned has not been effected and therefore even in*principle*not known with certainty.-**personal p.**an*idiosyncratic*judgment about the outcome of an*event*; it may include evidence too subtle to be disposed of in a*subjective*p..-the best*posterior*p.*rational**assessment*of the p. of an outcome on the*basis*of established knowledge modified and brought up to date. SEE ALSO: prior p.,*Bayes*theorem. Cf.:Bayes theorem.-**prior p.**the best*rational**assessment*of the p. of an outcome on the*basis*of established knowledge before the*present**experiment*is performed. For instance, the prior p. of the*daughter*of a*carrier*of*hemophilia*being herself a*carrier*of*hemophilia*is 1/2. But if the*daughter*already has an affected son, the*posterior*p. that she is a*carrier*is unity, whereas if she has a*normal*child, the*posterior*p. that she is a*carrier*is 1/3. See*Bayes*theorem.-a fair statement of the*subjective*p.*odds*that a*rational*, well-informed person would give or*take*for the outcome of an*experiment*. The*experiment*may be unique and not rationally understood (precluding both theoretically*sound*predication and*empirical*experience). The formulation is applicable to experiments that have been carried out but the outcome unknown. (For instance, a certain statement about the sex of the*fetus*early in*pregnancy*is established but perhaps not accessible until*amniocentesis*can be done.) Unlike personal probably, the*subjective*p. should be the same from all competent counselors in possession of the same evidence.* * *

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prob·a·bil·i·ty (prob″ə-bilґĭ-te) [L.*probabilis*probable, from*probare*to test or examine] the likelihood of occurrence of a specified event; it is often represented as a number between 0 (never) and 1 (always) that corresponds to the long-run trial at which an event occurs in a sequence of random independent trials under identical conditions, as the number of trials approaches infinity. Symbol*P.*

*Medical dictionary.
2011.*

**Synonyms**:

### Look at other dictionaries:

**Probability**— is the likelihood or chance 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… … Wikipedia**probability**— ► NOUN (pl. probabilities) 1) the extent to which something is probable. 2) a probable or most probable event. ● in all probability Cf. ↑in all probability … English terms dictionary**Probability**— Prob a*bil i*ty, n.; pl. {Probabilities}. [L. probabilitas: cf. F. probabilit[ e].] [1913 Webster] 1. The quality or state of being probable; appearance of reality or truth; reasonable ground of presumption; likelihood. [1913 Webster] Probability … The Collaborative International Dictionary of English**probability**— probability, probability distribution See distribution (statistical or frequency)}} ; sampling ; significance tests ; … Dictionary of sociology**probability**— [präb΄ə bil′ə tē] n. pl. probabilities [MFr probabilité < L probabilitas] 1. the quality or state of being probable; likelihood 2. something probable 3. Math. the ratio of the number of times something will probably occur to the total number… … English World dictionary**probability**— I noun anticipation, appearance of truth, believability, chance, conceivability, credibility, credibleness, expectation, fair chance, fair expectation, favorable chance, liability, liableness, likelihood, likeliness, odds, ostensibility,… … Law dictionary**Probability**— [engl.], Wahrscheinlichkeit … Universal-Lexikon**probability**— (n.) mid 15c., quality of being probable, from O.Fr. probabilite (14c.) and directly from L. probabilitatem (nom. probabilitas), from probabilis (see PROBABLE (Cf. probable)). Meaning вЂњsomething likely to be trueвЂќ is from 1570s; mathematical… … Etymology dictionary**probability**— [n] likelihood of something happening anticipation, chance, chances, conceivability, contingency, credibility, expectation, feasibility, hazard, liability, likeliness, odds, outside chance*, plausibility, possibility, practicability, prayer,… … New thesaurus**probability**— noun ADJECTIVE ▪ high, real, strong ▪ There is a high probability that it will snow tonight. ▪ greater, increased ▪ low … Collocations dictionary**probability**— The mathematics of probability is well understood. Probability is a non negative, additive set function whose maximum value is unity. What is harder to understand is the application of the formal notion to the actual world. One point of… … Philosophy dictionary