This article specifies a multilevel measurement model for survey response when data are nested. The model includes a test–retest model of reliability, a confirmatory factor model of interitem reliability with item-specific bias effects, an individual-level model of the biasing effects due to respondent characteristics, and a neighborhood-level model of construct validity. We apply this model for measuring informal social control within collective efficacy theory. Estimating the model on 3,260 respondents nested within 123 Seattle neighborhoods, we find that measures of informal control show reasonable test–retest and interitem reliability. We find support for the hypothesis that respondents’ assessments of whether their neighbors would intervene in specific child deviant acts are related to whether they have observed such acts in the past, which is consistent with a cognitive model of survey response. Finally, we find that, when proper measurement models are not used, the effects of some neighborhood covariates on informal control are biased upward and the effect of informal social control on violence is biased downward.