It is necessary or desirable to identify, check nonreturns and to permit associating responses with other data on the subjects. If such is the case, it is a clear violation of ethics to code response sheets surreptitiously or secretly to identify responders after stating or implying that responses are anonymous. In so doing, the investigator has in effect promised the responders that their responses cannot be identified. The very fact that at some point the responses can be identified fails to provide the promised security, even though the investigator intends to keep them confidential.

If a questionnaire contains sensitive questions yet must be identified for accomplishment of its purpose, the best policy is to promise confidentiality but not anonymity. In this case a code number should be clearly visible on each copy of the instrument, and the responders should be informed that all responses will be held in strict confidence and used only in the generation of statistics. Informing the responders of the uses planned for the resulting statistics is also likely to be helpful.