Aims: The Finnish Hospital Discharge Register (FHDR) is one of the oldest individual level hospital discharge registers and has been intensively used for research purposes. The aim of this study was to gather information concerning the quality of FHDR into one place in terms of a systematic review of validation studies that compare data to external information. Methods: Several reference databases were searched for validity articles published until January 2012. For each included study, focus of validation, register years examined, number of compared observations, external source(s) of data, summary of validation results, and conclusions concerning the validity of FHDR were extracted. Results: In total, 32 different studies comparing FHDR data to external information were identified. Most of the studies examined validity in the case of vascular disease, mental disorders or injuries. More than 95% of discharges could be identified from the register. Positive predictive value (PPV) for common diagnoses was between 75 and 99%. Conclusions: Completeness and accuracy in the register seem to vary from satisfactory to very good in the register as long as the recognised limitations are taking into account. Poor recording of subsidiary diagnoses and secondary operations and other rarely used items are the most obvious limitations in validity, but do not compromise the value of data in FHDR in being used in studies that are not feasible to conduct otherwise.
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