Abstract
Linked electronic healthcare databases are increasingly being used in observational research. The objective of this study was to investigate the impact of the choice of data source in estimating mortality following VTE, with a secondary aim to investigate the influence of the denominator definition. We used the UK Clinical Practice Research Datalink (CPRD) to identify patients aged 18+ with venous thromboembolism (VTE). Multiple cohorts were identified in order to assess how mortality rates differed with a range of data sources. For each of the cohorts, incidence rates per 1,000 person years (/1000py) and relative rates (RRs) of all-cause mortality were calculated. The lowest mortality rate was found when only primary care data were used for both the exposure (VTE) and the outcome (death) (108.4/1000py). The highest mortality rate was found for patients diagnosed in secondary care (237.2/1000py). When linked primary and secondary care data were included for eligible patients and for the overlapping period of data collection, a mortality rate of 173.2/1000py was found. Sensitivity analyses varying the denominator definition provided a range of results (140.6–164.3/1000py). The relative rates of mortality by gender and age were comparable across all cohorts. Depending on the choice of data source, the population studied may be different. This may have substantial impact on the main findings, in particular on incidence rates of mortality following VTE.
Highlights
Electronic healthcare data bases are increasingly being used in observational research
Each individual data source had a different period of coverage, the Clinical Practice Research Datalink (CPRD) linkage was limited to consenting GP practices from England, and not all of the patients registered at a participating practice were eligible for each linkage (Fig 1)
We looked at the impact of the choice of data source in estimating mortality following venous thromboembolism (VTE) and found considerable differences in the observed mortality rate across cohorts built using different sources, despite comparable relative rates by gender and age
Summary
Electronic healthcare data bases are increasingly being used in observational research. For conditions diagnosed, treated and managed solely in primary care, electronic healthcare records (EHR) from general practice may be a good source of data for pharmacoepidemiology studies.
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