  We study the influence of the centrality definition and detector efficiency
on the net-proton kurtosis for minimum bias Au+Au collisions at a beam energy
of $\sqrt{s_{\mathrm{NN}}}= 7.7$ GeV by using the UrQMD model. We find that
different ways of defining the centrality lead to different cumulant ratios.
Moreover, we demonstrate that the kurtosis is suppressed for central collisions
when a wider transverse momentum acceptance is used. Finally, the influence of
a detector efficiency on the measured cumulant ratios is estimated.
