It is important to make the questionnaire easy for the user to complete. There are two quite obvious reasons for this. First in order for the analysis to be statistically significant it is necessary to generate a high return rate. If users find difficulty in completing the questionnaire they might not complete it, and only a relatively small proportion will be returned. The second reason is that it is important to avoid ambiguity in the questions which are posed.
Ambiguous questions generate unreliable answers.
For both these reason, it is usual to trial the survey instrument with a small proportion of the intended population so that any design problems can be addressed before the main survey is carried out. The main advantages are the area and the flexibility of administration. They can be filled in at any time by any number of individuals. Because it is relatively easy to administer a large number of questionnaires, they are especially useful for comparing the opinions or understanding of a large number of users. The use of closed questions can prevent digressions.