Not necessarily, and it depends on how flexibility is defined. If “flexibility” is interpreted as “informal” (as opposed to “inflexible”, formal institutions), the Credibility Thesis predicts that one might encounter situations in which flexible institutions could lead to less investments, inasmuch as we would find situations in which they lead to more investments, or we find no influence at all. Similar confusion would result from studies into the relation between inflexible institutions and investment behavior. For the same reason, regression analyses aiming to correlate form to performance yield contradictory results (regardless whether we replace “flexibility” with “democracy” or “private property”, and “investments” with “GDP” or “price”).
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