  We selected mass-transferring binary candidates from the catalog of Kepler
eclipsing binary stars and investigated the dependence of the mass-transfer
rate on several astrophysical quantities, including orbital period, semi-major
axis, mass ratio, fill-out factor, temperature, and mass. We selected these
candidates using $O-C$ diagrams and calculated their mass-transfer rates.
Primary masses were obtained from the mass--temperature relation, and the
temperatures of the component stars were extracted from a catalog of
temperatures for Kepler eclipsing binary stars. The mass-transfer rates of
overcontact systems have associations with astrophysical quantities that seem
to differ from those of semi-detached or detached systems. These associations
indicate that mass exchange from more- to less-massive components (from less-
to more-massive components) generally becomes rapid (slow) as the mass exchange
evolves. However, for mass exchange from more- to less-massive components, this
tendency is not reasonable for binaries with a short period ($P<0.4$ d) and low
mass ($M_1<1.2$ M$_\odot$) because the correlations of these binaries are
opposite to those of binaries with long period and high mass. These different
correlations likely arise from differences in correlation between subtypes of W
UMa systems (i.e., W- and A-types). Alternatively, when mass exchange from
more- to less-massive components reoccurs after a mass-ratio reversal, its
properties may differ from those of the first mass exchange.
