The authors advance a theory of the effects of political institutions on st
ate policy. The theory explains how political institutions affect the abili
ty of leaders to maintain themselves in office, why some political systems
are more prone to policy failure than others, and why autocrats create mass
political systems. The key characteristics of institutions in this theory
are the sizes of a polity's selectorate and winning coalition. The authors
derive hypotheses from the theory and test those hypotheses using a data se
t covering more than 2,700 leaders from all states in the period from 1816
to 1990. The statistical tests demonstrate that (1) large winning coalition
s are associated with enhanced economic growth, (2) tenure is shortened by
a large winning coalition but lengthened by a large selectorate, and (3) in
the face of policy failure, leaders with a large selectorate are more like
ly to survive than those in systems with a large winning coalition. The aut
hors conclude by discussing the implications of these results.