  In general, synthesis models provide the mean value of the distribution of
possible integrated luminosities, this distribution (and not only its mean
value) being the actual description of the integrated luminosity. Therefore, to
obtain the closest model to an observation only provides confi- dence about the
precision of such a fit, but not information about the accuracy of the result.
In this contribution we show how to overcome this drawback and we propose the
use of the theoretical mean-averaged dispersion that can be produced by
synthesis models as a metric of fitting to infer accurate physical parameters
of observed systems.
