Assessing heterogeneity of electronic healthcare databases: a case study of background incidence rates of venous thromboembolism.

Large variability in IR between data sources and within age group and gender strata warrants the need for stratification and limits the feasibility of a meaningful pooled estimate. A more detailed knowledge of the data characteristics, operationalisation of case definitions and cohort population might support an informed choice of the adequate databases to calculate reliable estimates. This article is protected by copyright. All rights reserved.