The investigator makes a questionnaire pertaining to the field of investigation and sends it to the respondents, along with a covering letter, to collect information. A self-addressed stamped envelope is enclosed for returning the questionnaire by post.

Suitability

1. 1.When the field of investigation is very large.
2. 2.When respondents are literate and likely to co-operate.

Merits

• Wide Coverage: Used for extensive enquiries covering very wide area. Only method to reach remote areas.
• Economy: Requires less time, money and labour.
• Originality: Data are very much original because informants are directly involved.
• Free from bias: Every question interpreted by the respondent in own way. Free from investigator bias.
• Maintains secrecy: Suitable for sensitive questions, maintains anonymity.

Demerits

• ✗Limited Scope: Applicable only where respondents are educated.
• ✗Less Accuracy and Precision: Accurate answers may not be received if questions are difficult.
• ✗Lack of Interest: Some informants may not care to fill up the questionnaire. Large non-response makes conclusions impossible.
• ✗Chances of Misinterpretation: Informants may not understand correct sense of questions.
• ✗Time Consuming: Particularly when information is obtained by post.

Precautions

• Questionnaire should be simple, short and attractive.
• Questions should not hurt sentiments of informants.
• There should be system, sequence and proper planning in questions.
• Object of enquiry must be clearly defined.
• Efforts should be made to get information as early as possible.
• Self-addressed stamped envelope should be enclosed.