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Response Rates: The overall weighted response rate for the 2010 data collection for NISVS ranged from 27.5 percent to 33.6 percent. The computation of the weighted response rate reflected the stratified, two-phase, dual-frame survey design used in NISVS, and accounted for the disproportionate sampling across states, combined response rates from Phases One and Two, and combined response rates resulting from the two sampling frames. The range in the overall response rates reflects differences in how the proportion of the unknowns that are eligible is estimated. The 27.5 percent was an estimate of the proportion of the unknowns that are eligible based on the information identified by interviewers when calling numbers. The upper estimate (33.6 percent) also included information from the prescreening process.