  We investigate numerically and experimentally the statistics of the changes
in the amount of frequency splitting upon the adsorption of particles
one-by-one into the mode volume of whispering gallery mode (WGM) microresonator
and microlasers. This multiple-particle induced frequency splitting (MPIFS)
statistics carries information on the size and the number of adsorbed particles
into the mode volume, and it is strongly affected by two experimental
parameters, namely the WGM field distribution and the positions of the
particles within the mode volume. We show that the standard deviation and
maximum value of the MPIFS are proportional to the polarizability of the
particles, and propose a method to estimate particle size from the MPIFS if the
only available data from experiments is frequency splitting.
