The possibilities for biasing of mailed questionnaire results due to only partial returns are all too obvious. Nonreturners may well have their own peculiar views toward questionnaire content in contrast to their more cooperative corecipients. Thus it is strange that very few published accounts of questionnaire-based research report any attempt to deal with the problem. Some do not even acknowledge it.

There are ways of at least partially accounting for the effects of nonreturns after the usual follow-up procedures, such as postcard reminders. To the extent that responders are asked to report personal characteristics, those of returners may be compared to known population parameters. For example, the proportion of younger returners might be much smaller than the population proportion for people in this age group. Then results should be applied only cautiously with respect to younger individuals. Anonymous responses may be categorized according to postal origin (if mailed). Then results should be applied more cautiously with respect to underrepresented areas.

Usually, the best way to account for nonresponders is to select a random sample of them and obtain responses even at substantial cost. This is possible even with anonymous questionnaires, though, in this case, it is necessary to contact recipients at random and first inquire as to whether they returned the questionnaire. Telephone interviews are often satisfactory for obtaining the desired information from nonresponders, but it is almost always necessary to track down some nonresponders in person. In either case, it may not be necessary to obtain responses to all questionnaire items. Prior analyses may reveal that only a few specific questions provide a key to a responder's opinion(s).