This paper shows that the power law property of the firm size distribution is a robust prediction of the standard entry-exit model of firm dynamics. Only one variation is required: the usual restriction that firm productivity lies below an ad hoc upper bound is dropped. We prove that, after this small modification, the Pareto tail of the distribution is predicted under a wide and empirically plausible class of specifications for firm-level productivity growth. We also provide necessary and sufficient conditions under which the entry-exit model exhibits a unique stationary recursive equilibrium in the setting where firm size is unbounded.
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