Second, an important element of the AJR line of reasoning is that settler mortality reflects
past settlement policies and their modern consequences. Yet the instruments appear to be
correlated with the modern disease environment as well. Jeffrey Sachs and his associates (Gallup
et al. 2001, Kiszewski et al. 2004) present data on modern malaria risk and malaria ecology. The
correlation of the log of settler mortality with malaria risk is .67, and with malaria ecology it is .66.
The log of 1500 population density, however, has a correlation of .38 with malaria risk, but only
.14 with malaria ecology. These correlations raise the question of whether AJR instruments reflect
the historical rather than the modern disease environment, since the latter might have an
independent affect on human capital, development, and institutions.
AJR are well aware of this concern. As a test, they regress their preferred institutional
variables on settler mortality and malaria together, and find that settler mortality but not modern
malaria is statistically significant. Table 10 presents the results of similar regressions using all 23
available observations (AJR use a subset). Our results are different from those reported in their
work. The impact of settler mortality on today’s institutions remains significant, but so is that of
malaria risk. At least part of what settler mortality captures is the modern disease environment.
These results suggest that the issue of modern disease environment is real, and one should exercise
caution in treating AJR instruments as proxies for the colonial but not modern mortality risk.