In postal research the respondent is sent a questionnaire for self-completion through the post. The category also includes other means of distribution such as leaving questionnaires in hotel rooms, or giving them out as people enter museums or department stores. Perhaps 'self-completion' is a better descriptive term since the essence of the method is that the individual completes the questionnaire alone, and then returns it either through the post, or by leaving it in an indicated place. The fact that many of those sent or given self-completion questionnaires fail to return them is the major limitation of postal research. Response rates for completed questionnaires as low as 5 per cent are not uncommon, although the range is very wide. When topics are of particular interest to the sample the response may be much greater. An industrial distributor achieved 85 per cent response in a recent survey of customers, although this is unusually high. A well-run postal survey of interest to respondents, not too demanding of them, with some specific incentive for completion and with follow-up reminders, can expect to achieve a response rate of over 50 per cent.
Self-completion questionnaires work best when they are fully precoded so that all the respondent has to do is tick boxes. The layout should be clear and spacious. If the appearance of the questionnaire suggests that a lot of time will be needed to fill it in, it is less likely to be returned. For these reasons, the type of data that can be collected using postal research is limited in both quantity and quality. When a postal survey is used, evidence suggests that a covering letter explaining the purpose of the survey, and suggesting advantages for the respondent in co-operating, has a very important influence on the response rate. Normally, a second questionnaire is sent to non-responders about three weeks after the first, and then a third. These follow-ups are useful in pushing up the overall response rate. Some argue that separate analysis of the late responders from early responders will reveal differences in response, and that non-responders are likely to be further in the direction of late responders. This allows some subjective estimation to be made of the likely bias present in data from a non-representative sample. Essentially, those who return the questionnaire are self-selected, rather than selected by the researcher, and so may not be representative of the whole group. The lower the response rate, the more of a limitation this becomes. In practice, there is often a bias in such respondents, since individuals who feel more strongly about the topic under investigation are more likely to complete and return questionnaires about it.
Despite this limitation, postal research is quite widely used, for several reasons. It can reach all types of people, in all geographical areas, for the same cost, and does not involve personal interviewers. This makes it much less expensive than other methods. It is also comparatively speedy, since the majority of questionnaires will be returned within the first few weeks if they are going to be returned at all. Sometimes, postal research can be used to reach respondents who would not see an interviewer or accept a telephone call, particularly senior business and professional people. For certain basic factual types of data, postal research may be quite useful, and in these circumstances its advantages over other methods are most evident. The method is often used in industrial research. This is particularly so when an industrial supplier wants to identify ways in which services to customers can be improved. Customers are generally quite ready to respond to this type of research, which is in the interests of both parties. Whether postal research can be used depends on whether an appropriate and up-to-date mailing list exists. Once again, this explains why the method is used in business research, since either customer lists or classified business directories can be used, which make it possible to mail to selected types of company or regions. Whether for industrial or consumer application, postal surveys are most readily completed by enthusiasts and so certain subjects are more likely than others to be successful in using this method; for example, those addressed to specialist groups or concerned with hobbies.
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