University of Massachusetts Amherst researchers estimated that from 1970 to 1996, capital flight from 30 Sub-Saharan countries totaled $187bn, exceeding those nations' external debts. (The results, expressed in retarded or suppressed development, have been modeled in theory by economist Mancur Olson.) In the case of Africa, one of the factors for this behavior was political instability, and the fact that new governments often confiscated previous government's corruptly obtained assets. This encouraged officials to stash their wealth abroad, out of reach of any future expropriation. In contrast, Asian administrations such as Suharto's New Order often took a cut on business transactions or provided conditions for development, through infrastructure investment, law and order, etc.

Which researchers studied corruption from Sub-Saharan countries from 1970 to 1996?