  We study Sutton's `microcanonical' model for the internal organisation of
firms, that leads to non trivial scaling properties for the statistics of
growth rates. We show that the growth rates are asymptotically Gaussian in this
model, at variance with empirical results. We also obtain the conditional
distribution of the number and size of sub-sectors in this model. We formulate
and solve an alternative model, based on the assumption that the sector sizes
follow a power-law distribution. We find in this new model both anomalous
scaling of the variance of growth rates and non Gaussian asymptotic
distributions. We give some testable predictions of the two models that would
differentiate them further. We also discuss why the growth rate statistics at
the country level and at the company level should be identical.
