  We consider the problem of designing a prospective randomized trial in which
the outcome data will be self-reported, and will involve sensitive topics. Our
interest is in misreporting behavior, and how respondents' tendency to under-
or overreport a binary outcome might affect the power of the experiment. We
model the problem by assuming each individual in our study is a member of one
"reporting class": a truth-teller, underreporter, overreporter, or
false-teller. We show that the joint distribution of reporting classes and
"response classes" (characterizing individuals' response to the treatment) will
exactly define the bias and variance of the causal estimate in our experiment.
Then, we propose a novel procedure for deriving sample sizes under the
worst-case power corresponding to a given level of misreporting. Our problem is
motivated by prior experience implementing a randomized controlled trial of a
sexual violence prevention program among adolescent girls in Nairobi, Kenya.
