(To name and address)
Subject: (Purpose of the letter)
Respected (Recipient’s name),
(First Paragraph): Give an introduction about who you are and what responsibility you are undertaking through this questionnaire. Provide the purpose behind the survey. But be cautions not to mention what you are exactly looking for as this may bias the answers of the respondents to suit your requirements. Be open to share the results of the survey in return.
(Second Paragraph): Provide instructions to answer the questions while taking the survey. Mention that all information provided in this questionnaire by the respondent will be strictly confidential and will not be shared by any outside parties.
(Third Paragraph): Be open to not finding answers to some questions that the respondent is unable to answer. Request for fair and honest opinion from the respondent. And finally end the cover letter by thanking the respondent to make time and answering the survey.
(Enclose the questionnaire)