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1 Studies in the History of Statistics and Probability ... - Sheynin, Oscar

1 Studies in the History of Statistics and Probability ... - Sheynin, Oscar

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It does not exist always even if <strong>the</strong> pert<strong>in</strong>ent magnitudes are<strong>in</strong>tuitively <strong>in</strong>dependent. Statistical <strong>in</strong>dependence can only be discussedwith complete justification after establish<strong>in</strong>g statistical stability.Independence <strong>of</strong> a separate measurement is mean<strong>in</strong>gless. Non-correlation<strong>of</strong> pairs <strong>of</strong> magnitudes X 1 (s), ..., X n (s) means that E(X i , X j ) = 0 for i, j = 1, ..., n <strong>and</strong> i≠ j.2.6. The ma<strong>in</strong> problem <strong>of</strong> <strong>the</strong> applied <strong>the</strong>ory <strong>of</strong> probability. Afterheuristically forecast<strong>in</strong>g <strong>the</strong> <strong>in</strong>itial magnitude V, to predict <strong>the</strong>oretically somesecondary magnitude, <strong>the</strong>ir functions. Forecast<strong>in</strong>g <strong>the</strong> <strong>in</strong>itial magnitudes is always<strong>in</strong>tuitive.2.7. Limit <strong>the</strong>orems <strong>of</strong> <strong>the</strong> <strong>the</strong>ory <strong>of</strong> probability. For <strong>the</strong> central limit<strong>the</strong>orem (CLT) magnitudes X 1 (s), ..., X n (s) are considered statistically <strong>in</strong>dependentfor any n <strong>and</strong> <strong>the</strong>ir scatter around <strong>the</strong>ir expectations is supposed to be roughly <strong>the</strong>same. For <strong>the</strong> law <strong>of</strong> large numbers (LLN) <strong>the</strong> second dem<strong>and</strong> is dropped <strong>and</strong> <strong>the</strong>first one weakened so that variance can be even replaced by non-correlation. TheCLT is practically admitted if <strong>the</strong> LLN takes place <strong>in</strong>tuitively.Quantitative estimates dur<strong>in</strong>g <strong>the</strong> pro<strong>of</strong> <strong>of</strong> <strong>the</strong> laws <strong>of</strong> large numbersare only possible by means <strong>of</strong> <strong>the</strong> [Bienaymé −] Chebyshev <strong>in</strong>equalitybut <strong>the</strong>y are rough <strong>and</strong> <strong>in</strong>expedient as compared with <strong>the</strong> CLT. In <strong>the</strong><strong>in</strong>itial period <strong>of</strong> <strong>the</strong> development <strong>of</strong> <strong>the</strong> probability <strong>the</strong>ory <strong>the</strong>fundamental importance <strong>of</strong> limit <strong>the</strong>orems had been essentiallyexaggerated which is not completely done away with even now 2 . Thus,sometimes statements are made assert<strong>in</strong>g that statistical stability is dueto <strong>the</strong> LLN.2.8. The Mises approach. His <strong>in</strong>itial concepts are extremely close to be<strong>in</strong>gexperimental. Instead <strong>of</strong> stability <strong>of</strong> <strong>the</strong> empirical mean he postulates <strong>the</strong> existence <strong>of</strong>E(X) = lim E m (X), m → ∞.The pattern <strong>of</strong> an extended series is meant here. Particular cases are <strong>the</strong> def<strong>in</strong>ition <strong>of</strong>probability as <strong>the</strong> limit <strong>of</strong> frequency <strong>and</strong> <strong>of</strong> F(X) be<strong>in</strong>g <strong>the</strong> limit <strong>of</strong> F m (X). Theconvergence can be understood <strong>in</strong> different ways.R<strong>and</strong>omness (that is, unpredictability) does not enter directly, <strong>the</strong>whole arsenal <strong>of</strong> tools is typically ma<strong>the</strong>matical. In similar ways,ma<strong>the</strong>maticians discuss derivatives <strong>and</strong> <strong>in</strong>tegrals ra<strong>the</strong>r than velocitiesor specific heat. Transitions to <strong>the</strong> limit are only <strong>the</strong> means (ornecessary! expenses) <strong>of</strong> a rigorous formalization 3 . The Mises approachprovides civil rights <strong>in</strong> <strong>the</strong> <strong>the</strong>ory <strong>of</strong> probability for <strong>the</strong> knownempirical patterns <strong>of</strong> treat<strong>in</strong>g data dat<strong>in</strong>g back to <strong>the</strong> very foundations<strong>of</strong> <strong>the</strong> natural scientific method with its dem<strong>and</strong> <strong>of</strong> repeatedreproduction <strong>of</strong> results.The ma<strong>in</strong> feature <strong>of</strong> <strong>the</strong> Mises approach consists <strong>in</strong> deal<strong>in</strong>g wi<strong>the</strong>veryth<strong>in</strong>g as though consider<strong>in</strong>g an experiment. Not surpris<strong>in</strong>gly,expectation is <strong>in</strong>troduced <strong>in</strong> applications accord<strong>in</strong>g to his postulate<strong>of</strong>ten without cit<strong>in</strong>g Mises.2.9. Comparison with <strong>the</strong> Kolmogorov axiomatization. TheMises approach most likely can not be <strong>in</strong>cluded with<strong>in</strong> <strong>the</strong> boundaries<strong>of</strong> this axiomatization. The ma<strong>in</strong> <strong>the</strong>oretical problem apparentlyconsists <strong>in</strong> discover<strong>in</strong>g existence <strong>the</strong>orems for number sequencesconverg<strong>in</strong>g to <strong>the</strong> given beforeh<strong>and</strong> distribution function. Thisproblem is still only solved for weak convergence (Postnikov 1960).The Mises approach should be specially developed by number<strong>the</strong>oreticmethods unusual for <strong>the</strong> Kolmogorov axiomatics.126

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