  In order to explain the origin of skewness in the gamma-ray burst (GRB)
duration distribution, a statistical model, based on the cosmological time
dilation and taking into account the GRB formation rate and instrumental
effects, is examined. It is concluded that the considered effects are able to
account for only a small fraction of the observed skewness. Therefore, its
origin needs to be searched for in the processes governing the progenitors of
GRBs.
