Another design limitation concerns the cooperation rates, which, though typical of recent U.S. telephone surveys, are lower than those for many face-to-face surveys (Midanik and Greenfield, 2003b). Because telephone break-offs often occur prior to identification of the study topic, low response rates in telephone surveys may introduce less bias than they would in face-to-face interviews (Groves, 2006). Also, two types of evidence argue against nonresponse bias in the NAS. First, an extensive series of methodological studies comparing identical questions in telephone and in-person surveys has found comparable estimates across modalities for alcohol consumption (Greenfield et al., 2000; Midanik and Greenfield, 2003a,b) and only modest and inconsistent mode effects for alcohol harms (Midanik et al., 2001), despite higher response rates for in-person surveys. Second, analyses examining the 2000 and 2010 NAS sample replicates (each replicate being a random subsample with a specific response rate varying around the overall mean) found no association between replicate response rate and respondent demographics, alcohol consumption, or alcohol problems. Still, it seems possible that representation of the most disadvantaged populations (e.g., the incarcerated, those living in poverty) was compromised. This could have biased estimates of alcohol problems downward, particularly for racial/ethnic minorities (Grant et al., 2015).
