Effect on Mail Survey Return Rates of Including Questionnaires with Follow-up Letters

To study response rate a total of 2,002 questionnaires were mailed to respondents who were allocated to one of seven treatments. One treatment was a control group who received only an initial mailing (questionnaire and cover letter). The remaining six treatments were defined by two crossed factors, the number of follow-up waves of mailings (one, two, or three) and whether the follow-up mailings included only a reminder letter or a letter and another copy of a questionnaire. The results suggest more than one follow-up with a questionnaire is needed. A letter only was an ineffective method.