ASSESSMENT OF WEIGHTING METHODOLOGY FOR THE NATIONAL COMORBIDITY SURVEY

The authors studied weighting adjustments for the National Comorbidity Survey (1990-1992), a large-scale national epidemiologic investigatio n of the prevalence, risk factors, and consequences of psychiatric mor bidity and comorbidity in the United States. Weighting adjustments for differential selection within households, new construction, unit nonr esponse, and poststratification were examined separately and in combin ation. Specific issues addressed included the magnitude of the bias in curred from ignoring the weights, the added variance from weighting an d how well this was predicted by simple formulae, and the performance of methods for trimming the weights. Weights had quite modest effects on point estimates of prevalences but resulted in major increases in v ariance unless trimmed, The weights after trimming and poststratificat ion appeared to work well. It is suggested that the added variance fro m weighting be carefully monitored in similar surveys. Alternatives to the use of trimming for controlling variance are worth exploring.