  Initial volume fluctuation (VF) caused by participant fluctuation would be
the background which should be subtracted from experimentally measured
higher-order cumulants. STAR experiment has been applied Centrality Bin Width
Correction (CBWC) to suppress VF. However, CBWC is not perfect method, there
might be thus residual fractions of VF backgrounds. Recently, Volume
Fluctuation Correction (VFC) was developed under the assumption of the
independent particle production (IPP) model. In this talk, the importance of
subtracting VF and validity of the VFC are studied by using simple toy models
assuming IPP as well as UrQMD model. The results showed that VFC worked well in
toy model but did not work well in UrQMD which imply that IPP model could be
broken in UrQMD.
