What are the advantages and disadvantages of online questionnaire?

The main advantage of mail questionnaires is that a wide geographical area can be covered in the survey. They are mailed to the respondents who can complete them at their convenience in their homes and at their own pace. However the return rates of mail questionnaire are typically low. A 30% response rate is considered acceptable. Another disadvantage of the mail questionnaire is that any doubts the respondents might have cannot be clarified.