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American Journal of Epidemiology Vol. 130, No. 2: 371-378
Copyright © 1989 by The Johns Hopkins University School of Hygiene and Public Health

research-article

A METHOD FOR COMBINING MATCHED AND UNMATCHED BINARY DATA

APPLICATION TO RANDOMIZED, CONTROLLED TRIALS OF PHOTOCOAGULATION IN THE TREATMENT OF DIABETIC RETINOPATHY

STEPHEN W. DUFFY1,, THOMAS E. ROHAN2 and DOUGLAS G. ALTMAN3

1MRC Biostatistics Unit Cambridge, England
2NCIC Epidermiology Unit, Faculty of Medicine, University of Toronto Toronto, Ontario, Canada
3Medxal Statistics Laboratory, Imperial Cancer Research Fund, Lincoln's Inn Fields London, England

Reprint requests to Stephen W. Duffy, MRC Biostatistics Unit, 5 Shaftesbury Road, Cambridge CB2 2BU, England.

A method for combining matched and unmatched data is described and was applied to the results of randomized, controlled trials of photocoagulation in the treatment of diabetic retinopathy. A pooled estimate from the matched and unmatched studies war obtained by adaptation of the Mantel-Haenszel method, where the strata were unmatched studies and matched pairs within studies. A test of significance was based on the Mantel-Haenszel chi-square statistic, the latter also being used to calculate test-based confidence intervals. A test of homogeneity was performed by combining Mantel-Haenszel chi-square statistics from the matched and unmatched studies. By these methods, the combined estimate of the risk of deterioration of visual acuity for those receiving photocoagulation (relative to a risk of unity for those not receiving photocoagulation) was 0.37 (95 per cent confidence interval 0.29–0.46). The chi-square statistic (1 df) for an effect of treatment was 87.75 (p < 0.0001). The chi-square statistic for homogeneity of relative risk among studies was 11.20 (4 df, p < 0.05). However, this result was influenced disproportionately by one small matched study.

epidemiologic methods;; statistics


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