  We investigate the measurement of the sixth order cumulant and its ratio to
the second order cumulant ($C_6/C_2$) in relativistic heavy-ion collisions. The
influence of statistics and different methods of centrality bin width
correction on $C_6/C_2$ of net-proton multiplicity distributions is
demonstrated. There is no satisfactory method to extract $C_6/C_2$ with the
current statistics recorded at lower energies by STAR at RHIC. With statistics
comparable to the expected statistics at the planned future RHIC Beam Energy
Scan II (BES II), no energy dependence of $C_6/C_2$ is observed in central
collisions using the UrQMD model. We find if the transition signal is as strong
as predicted by the PQM model, then it is hopefully observed at the upcoming
RHIC BES II.
