Scaled variance as a function of \aveNpart for charged-particle multiplicity distributions and background fluctuations ($\omega_{\rm ch}^{\rm back}$) based on aparticipant model calculation for $|\eta| < 0.5$ The expectation from Poisson-like particle production is indicated by the dotted line. The statistical uncertainties are smaller than the size of the markers. The systematic uncertainties are presented as filled boxes.