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The propensity theory of probability is one interpretation of the concept of probability. Theorists who adopt this interpretation think of probability as a physical propensity, or disposition, or tendency of a given type of physical situation to yield an outcome of a certain kind, or to yield a long run relative frequency of such an outcome.〔'Interpretations of Probability', Stanford Encyclopedia of Philosophy (). Retrieved 23 December 2006.〕 Propensities are not relative frequencies, but purported ''causes'' of the observed stable relative frequencies. Propensities are invoked to ''explain why'' repeating a certain kind of experiment will generate a given outcome type at a persistent rate. A central aspect of this explanation is the law of large numbers. This law, which is a consequence of the axioms of probability, says that if (for example) a coin is tossed repeatedly many times, in such a way that its probability of landing heads is the same on each toss, and the outcomes are probabilistically independent, then the relative frequency of heads will (with high probability) be close to the probability of heads on each single toss. This law suggests that stable long-run frequencies are a manifestation of invariant ''single-case'' probabilities. Frequentists are unable to take this approach, since relative frequencies do not exist for single tosses of a coin, but only for large ensembles or collectives. Hence, these single-case probabilities are known as propensities or chances. In addition to explaining the emergence of stable relative frequencies, the idea of propensity is motivated by the desire to make sense of single-case probability attributions in quantum mechanics, such as the probability of decay of a particular atom at a particular time. The main challenge facing propensity theories is to say exactly what propensity ''means''. And then, of course, to show that propensity thus defined has the required properties. At present, unfortunately, none of the well-recognised accounts of propensity comes close to meeting this challenge. ==History== A propensity theory of probability was given by Charles Sanders Peirce.〔Peirce, Charles Sanders and Burks, Arthur W., ed. (1958), the ''Collected Papers of Charles Sanders Peirce'' Volumes 7 and 8, Harvard University Press, Cambridge, MA, also Belknap Press (of Harvard University Press) edition, vols. 7-8 bound together, 798 pages, (online via InteLex ), reprinted in 1998 Thoemmes Continuum.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「propensity probability」の詳細全文を読む スポンサード リンク
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