  We investigate degree of coherence of pion sources produced in relativistic
heavy ion collisions using multi-particle interferometry. In order to obtain
``true'' chaoticity, lambda^true from two-pion correlation functions measured
in experiments, we make a correction for long-lived resonance decay
contributions. Using this lambda^true and the weight factor which are obtained
from parameter fitted to two- and three-pion correlation function, we calculate
a chaotic fraction epsilon and the number of coherent sources alpha for
different colliding energies. The result gives constraints on the source and
shows an increase of the minimum number of alpha with multiplicity, although
multiplicity independent chaoticity is not excluded.
