Validation and validity of diagnoses in the General Practice Research Database: a systematic review

AIMS To investigate the range of methods used to validatediagnoses in the General Practice ResearchDatabase (GPRD), to summarize findings and to assess the quality of these validations. METHODS A systematic literature review was performed by searching PubMed and Embase for publications usingGPRD data publishedbetween 1987 and April 2008. Additional publications were identified from conference proceedings, back issues of relevant journals, bibliographies of retrieved publications and relevant websites. Publications that reported attempts to validatedisease diagnoses recorded in the GPRD were included. RESULTS We identified 212 publications, often validatingmore than one diagnosis. In total, 357 validationsinvestigating 183 different diagnoses met our inclusion criteria. Of these, 303 (85%) utilized data from outside the GPRD to validatediagnoses. The remainder utilized only data recorded in the database. The median proportion of cases with a confirmed diagnosis was 89% (range 24-100%). Details of validationmethods and results were often incomplete. CONCLUSIONS A number of methods have been used to assess validity. Overall, estimates of validitywere high. However, the quality of reporting of the validationswas often inadequate to permit a clear interpretation. Not all methods provided a quantitative estimate of validityand most methods considered only the positive predictive value of a set of diagnostic codes in a highly selected group of cases. We make recommendations for methodology and reporting to strengthen further the use of the GPRD in research.