Application of Survival Analysis Techniques to Evaluation of Factors Affecting Compliance in a Clinical Trial of Hypertension Control E. O. Smith, R. J. Hardy, G. R. Cutter, J. D. Curb, and C. M. Hawkins From the School of Public Health, The University of Texas, Houston, Texas ABSTRACT: Survival analysis techniques including follow-up life tables and regression methods that utilize concomitant information are shown to be applicable to the analysis of medical follow-up study dropout data. These techniques have been applied to data from the Hypertension Detection and Follow-up Program in order to gain knowledge about factors associated with a study participant's tendency to either remain active in the Program or drop out. INTRODUCTION Increasing attention has been focused on patient compliance with therapeu- tic regimens in recent years. The contribution of patient compliance to the success or failure of therapeutic regimens and public health programs has been shown to be surprisingly large. In addition, patient compliance is important to the design, analysis, and interpretation of clinical trials. This type of problem is, however, dealt with in many elementary statistics text under the heading of missing data. These methods are useful in small studies where the number of missing data are very small. Feinstein [1] addresses the issue of compliance and gives an analytical review of the subject. He points out the impact of noncompliance or partial compliance on data analysis as well as some of the pitfalls involved in interpreting data from a selected compliant population. Interest in the problem has increased in recent years with the advent of large multicenter trials, often depending on behavioral change. The potential for bias and inference problems due to noncompliance in these essentially nonrepeatable studies with their enor- mous impact on the scientific community and their enormous cost is not small. Although the cost of attaining the cooperation of those "reluctant Address requests for reprints to Dr. E. O'Brian Smith, Beta Blocker Heart Attack Trial, Coordinating Center, The University of Texas, School of Public Health, Houston, TX 77030. Received February 6, 1979; revised and accepted October 3, 1979. ControlledClinical Trials1, 59-69 (1980) 59 © Elsevier NorthHolland,Inc.,1980 0197-2456/80/01005911502.25