We analyze the proof of Bell's inequality and demonstrate that this inequal
ity is related to one particular model of probability theory, namely Kolmog
orov measure-theoretical axiomatics from 1933. We found a (numerical) stati
stical correction to Bell's inequality. Such an additional term epsilon(phi
) on the right-hand side of Bell's inequality can be considered as a probab
ility invariant of a quantum state phi. This is a measure of nonreproducibi
lity of hidden variables in different runs of experiments. Experiments to v
erify Bell's inequality can be considered as just experiments to estimate t
he constant epsilon(phi). It seems that Bell's inequality could not be used
as a crucial reason to deny local realism. We consider deterministic as we
ll as stochastic hidden variables models. (C) 2000 American Institute of Ph
ysics. [S0022-2488(00)01504-8].