Is the questionnaire to be completed at home, in a clinic or by telephone? If the questionnaire is to be completed at home, this has the advantage that there is more time to complete it than in a clinic or by telephone.

In a clinic situation, the time available to complete the questionnaire may be limited, being dependent upon what other questionnaires and examinations are to be completed during the same time period. If dealing with middle-aged or elderly subjects, it is advisable to warn them beforehand if they are to complete the questionnaire themselves, otherwise they may forget to bring reading glasses with them. It is also advisable to ensure that someone is available to help those who are unable to complete the questionnaire themselves. If subjects are not normally involved in shopping and cooking, they may not be able to adequately answer questions about their food intake. In this case, it may be better if the questionnaire is completed at home, with the person responsible for shopping and cooking.

If the questionnaire is to be completed by telephone, it is advisable to establish at the beginning of the interview that the call is at a convenient time and to advise each subject how long the interview is likely to take. This may help to reduce the potential for ill-considered answers if the subject does not have sufficient time to complete the interview comfortably.