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A measure of how likely something is to occur expressed as a decimal lying between 0 (cannot occur) and 1.0 (certain to occur) and can be associated with random variables defined for a particular population – an expression of the degree of certainty about the occurrence of particular events; the number of ways a particular event can occur divided by the number of possible outcomes (if all outcomes had an equal chance of occurring) and is a measure of what is to be expected over the long run; it is used to express degrees of belief or to refer to the strength an actor’s belief in a certain proposition and as a reflection of previous frequency of occurrence. The probability of throwing ‘seven’ in one throw of a pair of dice is 0.1666 – it is known that if two fair dice are thrown on many individual trials in approximately one sixth of these throws ‘seven’ will result. Similarly actuarial tables have been compiled concerning people’s death rates – the probability one has if aged between twenty and thirty that one will still be alive at seventy is around 42 per cent, that is, for every one hundred people between the ages of twenty and thirty forty two will survive ‘til age seventy. The later probability, since it is related to frequency, is ‘elastic’ in that the numbers of people surviving to various ages is affected by various dynamic factors such as improvements in modern medicine or a reduction in the numbers of people killed in car crashes, etc., and will vary somewhat – such that the equivalent statistical probabilities for survival one hundred years ago would have been markedly different. The assumption is made that the past frequency of events may be used to predict or to derive a probability for the event’s future occurrence. In the dice example the probabilities will be invariant on the assumption that the important variables involved in dice-throwing will not be changed, for example, dice shape, balance, etc.
In experimental science researchers conducting statistical analyses of data – collected from systematic observations and measurements so as to decide whether a particular hypothesis can be confirmed – apply the concept of probability to estimate the likelihood that some research result happened by chance. That an observed difference between groups in a study is due to chance might be found to be of very low probability, that is, a statistically significant result.
In a psychological context the frequency of observed events is used to estimate the probability of the events’ future occurrence. The evaluation of probability also has a relation with rational decision-making – to act rationally the probabilities of events should be a relevant concern for decision-makers.
(see also: Bayes' theorem, Laws of Probability » Probability theory, Probabilistic principle, likelihood, chance, random, standard deviation, distribution, generalizability»generalization, statistical decision-making) Back to: Glossary A-Z
Glossary of selected Judgement & Decision-making, Belief-related, and other Psychology terms A-Z » Labels:
Probability, probable, probably |