event-by-event fluctuations of these observables as well. And indeed, a first comparison suggests that this might be possible for the sample of most central events. Global conservation laws, imposed on a statistical system, lead, even in the large volume limit, to suppressed fluctuations. The multiplicity distributions of charged hadrons recently reported [@NA49_fluc] by the NA49 SPS experiment are systematically narrower than a Poissonian reference distribution. This could be interpreted [@MCEvsData] as effects due to energy and charge conservation in a relativistic hadronic gas.

Multiplicity fluctuations are usually quantified by the ratio of the variance of a multiplicity distribution to its mean value, the so-called scaled variance. In statistical models there is a qualitative difference in the properties of mean value and scaled variance. In the case of the mean multiplicity results obtained within the grand canonical ensemble (GCE), canonical ensemble (CE), and micro-canonical ensemble (MCE) approach each other in the large volume limit. One refers here to as the thermodynamic equivalence of these ensembles. It was recently found [@CEfluc1] that corresponding results for the scaled variance are different in different ensembles, and thus this observable is sensitive to conservation laws obeyed by a statistical system.

The growing interest in the 