Collecting data by mailing questionnaire methods is quite popular, particularly in case of big enquiries. It is being adopted by private individuals, research workers, private and public organizations and even by Government organizations. In this method a questionnaire is sent usually by post to the persons concerned with a request to answer the questions and return the questionnaire.
A questionnaire consists of a number of questions printed or typed in a definite order on a form or set of forms. The questionnaire is mailed to respondents who are expected to read and understand the questions and write down the reply in
the space meant for the purpose in the questionnaire itself. The respondents have to answer the questions on their own. The method of collecting data by mailing the questionnaires to respondents it most extensively employed in various economic and business surveys.The merits of this methods were there is low cost even when the universe is large and
is widely spread geographically. It is free from the bias of the interviewer answers are in respondents own words. Respondents have adequate time to give well thought out answers. Respondents, who are not easily approachable, can also be reached conveniently. Large samples can be made use of and thus the results can be made more dependable and reliable.
The main demerits of this method include low rate of return of the duly filled questionnaires. It can be used only when respondents are literate and cooperating. The control over questionnaire may be lost once it is sent. There is inbuilt inflexibility because of the difficulty of amending the approach once questionnaires have been dispatched. There is also the possibility of ambiguous replies or omission of replies altogether to certain questions, interpretation of omissions is difficult. It is difficult to know whether willing respondents are truly representative.