Factor Interaction Effects in Mail Survey Response Rates

Researchers have investigated the effectiveness of a wide range of variables in their attempts to increase the response rates for mail questionnaire surveys. Among these variables are: monetary incentives (both large and small), advance letters, stamped vs. business reply envelopes, timing of follow-up mailings, printed vs. mimeographed questionnaire forms, and personal vs. nonpersonal wordings of cover letters 1, 2, 4-10. In such investigations, a controlled experimental design is typically used to determine the effect of the one variable under study. Little attention has been given to a second important consideration-determining whether significant interaction effects exist among two or more factors applied simultaneously to increase the response rate. This latter area can be important since, for example, individual factors which improve response rates may in combination with other factors actually reduce the response. This study employs a 24 (four factors each at two levels) factorial design to identify the relationships existing among four variables previously used to increase the response rates in mail questionnaire surveys.