Interim Response to a Mail Questionnaire: Impacts on Variable Relationships*

Nagging doubts continue on the utility of the mail questionnaire, although advances in this technique provide response rates of 70 percent or higher. Return bias, a factor in attacks on the mail questionnaire, has been depicted as a necessary evil of such magnitude that the technique should be abandoned. But few studies using mail questionnaires have examined the impact of interim response on variable relationships. To test for return bias, data are reported from 931 residents of five small Iowa communities. Four mail requests elicited a 78.2 percent completion rate; interviews were attempted with terminal mail nonrespondents, yielding a final response rate of 92.8 percent. In a statistical sense, only minor differences are evident on correlation coefficients and unstandardized regression coefficients for the first and second response waves compared with data accumulated for all respondents. But when substantive conclusions are examined, the impact of interim response does not subside until the first three response waves are accumulated. Thus, attention must be given to the potential influence of return bias in mail-questionnaire studies, but calls for discontinuing use of the technique are unwarranted.