For example, age and income may be grouped into classes. In many studies the researcher may need to recontact the subject for follow-up information or to deliver the results of the study. Data sets from the same individual may need to be linked. The researcher may temporarily identify responses and remove the subject names as soon as the data are analyzed. Names may be coded and the identifying list be kept in a safe or separate area from the study data.
Some studies use aliases to protect the identity of subjects.
If direct contact with the subject is not appropriate, a second or third party may be recruited for data collection. Data should be stored in files accessible only to the investigator and his or her assistants. If computers are used to store data, the investigator must be certain that access to sensitive files is limited. Audiotapes and videotapes may be particularly revealing and require special precautions to maintain confidentiality when airing or viewing and for storage. If research is published, the investigator is accountable for the results and may be required to keep the data available for five to ten years.