Selection bias from requiring patients to give consent to examine data for health services research.

BACKGROUND: New rulings nationwide require health services researchers to obtain patient consent before examining personally identifiable data. A selection bias may result if consenting patients differ from those who do not give consent.

OBJECTIVE: To compare patients who consent, refuse, and do not answer.

DESIGN: Patients completing an in-office survey were asked for permission to be surveyed at home and for their records to be reviewed. Survey responses and practice billing data were used to compare patients by consent status.

SETTING: Urban family practice center.

PATIENTS: Of 2046 eligible patients, 1106 were randomly selected for the survey, were approached by staff, and agreed to participate. Approximately 87% of the nonparticipants were eliminated through a randomization process.

MAIN OUTCOME MEASURE: Consent status.

RESULTS: A total of 33% of patients did not give consent: 25% actively refused, and 8% did not answer. Consenting patients were older, included fewer women and African Americans, and reported poorer physical function than those who did not give consent (P<.05). Patients who did not answer the question were older, included more women and African Americans, and were less educated than those who answered (P<.02). Visits for certain reasons (eg, pelvic infections) were associated with lower consent rates. On multivariate analysis, older age, male sex, and lower functional status were significant predictors of consent.

CONCLUSIONS: Patients who release personal information for health services research differ in important characteristics from those who do not. In this study, older patients and those in poorer health were more likely to grant consent. Quality and health services research restricted to patients who give consent may misrepresent outcomes for the general population. Arch Fam Med. 2000;9:1111-1118