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By separating respondents in a survey of farmers into those who refused to be interviewed and were converted, those who were hard to reach, and those who gave no problems, we can estimate nonresponse bias from refusers not converted and respondents not reached. We show that for attitude questions the refusal bias is serious, ranging from 2 to 4 percent on many attitudes, and very often larger than the standard error in surveys of ordinary size.
Stinchcombe et al. (Thu,) studied this question.