Fourth National Incidence Study of Child Abuse and Neglect (NIS–4)

2.6 Weighting and Estimation 14The national estimates derive from weighted totals of the sampled children,with each child’s weight based on the probability of having selected the source thatreported the child to the study. The final weights are complex because they:• account for the differential selection probabilities for the sample unitsat each successive sampling stage;• compensate for agency nonresponse, and for incomplete or partialparticipation by sentinels and CPS agencies;• adjust for multiple probabilities of identifying the same maltreated childthrough multiple reports to CPS or through multiple sentinel sources;and• include an annualization multiplier to allow the reference-period data torepresent a full-year and to account for seasonality differences betweenthe two study reference periods (fall 2005, spring 2006).Base weights and base weight adjustments. For each sample unit in thestudy (county, agency, sentinel, and case), the base weight is the reciprocal of theprobability of including the unit in the sample. The NIS–4 also applied special weightingadjustments, including adjustments to ensure that study estimates are accurate relative tothe size and distribution of the child population at the time of the NIS–4 referenceperiods, taking into account that the U.S. child population was larger during the NIS–4reference periods than it was at the time of the 2000 census (when sampling probabilitieswere set) and that the distribution had shifted somewhat as well (especially as a result ofhurricanes Katrina and Rita).Nonresponse adjustments. Adjusting base weights for nonresponsecompensated for lost data. The NIS–4 had three types of nonresponse: nonparticipatingsentinel agencies, refusals or incomplete participation by sentinels, and missing CPS14Appendix A summarizes the NIS–4 weighting and estimation procedures. The NIS–4 Analysis Report(Sedlak, Mettenburg, Winglee et al., 2010) provides additional detail.2–16