  It is pointed out that in doing the factorial moment analysis with
non-integer partition $M$ of phase space, the influence of the phase-space
variation of two- (or more-) particle correlations has to be considered
carefully. In this paper this problem is studied and a systematic method is
developed to minimize this influence. The efficiency and self-consistency of
this method are shown using the data of 250 GeV/$c$ $\pi^+$p and K$^+$p
collisions from the NA22 experiment as example.
