Nonresponse was slightly higher in the Northeast (32%) compared with the West (25%), Midwest (21%), and South (24%), and the poststratification sampling weights adjusted for this differential nonresponse. An additional 7.89% of Wave III respondents refused to provide a urine specimen. 43 We performed sensitivity analyses to assess the total effect of nonresponse combined with imperfect sensitivity and specificity of the PCR assay (Table 3 ).