Quasi-Probability: Why quasi-Monte-Carlo methods are statistically valid and how their errors can be estimated statistically

Abstract

The classical model of probability theory, due principally to Kolmogorov, defines probability as a totally-one measure on a sigma-algebra of subsets (events) of a given set (the sample space), and random variables as real-valued functions on the sample space, such that the inverse images of all Borel sets are events. From this model, all the results of probability theory are derived. However, the assertion that any given concrete situation is subject to probability theory is a scientific hypothesis verifiable only experimentally, by appropriate sampling, and never totally certain. Furthermore, classical probability theory allows for the possibility of "outliers"—sampled values which are misleading. In particular, Kolmogorov's Strong Law of Large Numbers asserts that, if, as is usually the case, a random variable has a finite expectation (its integral over the sample space), then the average value of N independently sampled values of this function converges to the expectation with probability 1, as N tends to infinity. This implies that there may be sample sequences (belonging to a set of probability 0) for which this convergence does not occur; these are the "outliers".