An anonymous study is one in which nobody (not even
the researcher) can identify who provided data. It is
difficult to conduct an anonymous questionnaire through
the mail because of the need to follow-up on
nonresponders. The only way to do a follow-up is to mail
another survey or reminder postcard to the entire sample.
However, it is possible to guarantee confidentiality,
where those conducting the study promise not to reveal
the information to anyone. For the purpose of follow-up,
identifying numbers on questionnaires are generally
preferred to using respondents' names. It is important,
however, to explain why the number is there and what it
will be used for.
Some studies have shown that response rate is affected
by the anonymity/confidentiality policy of a study.
Others have reported that responses became more distorted
when subjects felt threatened that their identities would
become known. Others have found that anonymity and
confidentiality issues do not affect response rates or