Does excluding patients without telephones affect the results of telephone reminder studies?

Studies of the effectiveness of telephone reminders to improve the rate of appointments kept have shown conflicting results. Few have accounted for patients without telephones. We conducted a controlled clinical trial to study the effect of excluding patients without telephones in a study of telephone reminders in an urban pediatric clinic. Telephone reminders were attempted the evening before scheduled visits for 238 subjects; 259 controls received no reminders. The overall rate of kept appointments was the same (54%) for both the intervention group and the control group. In neither group was there a substantial difference in the "show" rate between patients with and without telephones (intervention group 52% versus 57%, control group 55% versus 54%). In the intervention group, the show rate was higher for those with telephones who were contacted (66%) than for those who were not (37%) (P < .001). Telephone reminders did not improve the overall rate of kept appointments but appeared to result in a significant improvement in the show rate of those who could be reached. Excluding patients who could not be reached by telephone may affect the usefulness of previous studies.