  We propose a method to test for the presence of differential ascertainment in
case-control studies, when data are collected by multiple sources. We show
that, when differential ascertainment is present, the use of only the observed
cases leads to severe bias in the computation of the odds ratio. We can
alleviate the effect of such bias using the estimates that our method of
testing for differential ascertainment naturally provides. We apply it to a
dataset obtained from the National Violent Death Reporting System, with the
goal of checking for the presence of differential ascertainment by race in the
count of deaths caused by child maltreatment.
