example, ascertaining African American study participants from one part of the United States and obtaining African American public controls ascertained from another location could introduce systematic differences and spurious findings due to differing types/levels of admixture or differences in environmental risks. Thus, the potential benefit of using public controls in terms of improving statistical power due to increased sample size must be weighed in each particular circumstance against the increased complexity of analyses and the potential loss of power due to poor imputation or other systematic problems arising from differently recruited cases and controls.
