Improved imputation of non-responses to mailback questionnaires.

Poor response rates, perhaps as low as 10 to 30 per cent, certainly bring into question the validity of any survey suffering such a malady. Repeated mailouts are capable of providing information on those persons who are resistant to responding. If one is willing to assume an exponential drop-off in response rates, then imputation is possible for the entire group of non-responders. Furthermore, a second exponential drop-off in favourable (or non-favourable) responses to particular items within the questionnaire leads to closed form estimates of population parameters and their associated standard errors. Three or more mailouts also provide a test of validity of the model assumed.