National and cross national comparative (CNC) drug utilization studies provide valuable information to policy makers to plan future measures to further enhance the quality and efficiency of their prescribing. Data sources for drug utilization (DU) studies include administrative databases, patient registries, electronic health records, and commercial databases.
However, CNC studies can be challenging as there can be differences in the data collected, e.g. whether dealing with reimbursed or total medicine utilization, including over-the-counter medicines; whether including all sectors or just inpatient or ambulatory care sectors; whether using similar units to measure and contrast utilization and expenditure data; and whether dealing with aggregated sales data or patient level data. [...]

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Expert Review of Pharmacoeconomics & Outcomes Research
Erasmus School of Health Policy & Management (ESHPM)

Garuoliene, K., Godman, B., Gulbinovič, J., Schiffers, K., & Wettermark, B. (2016). Differences in utilization rates between commercial and administrative databases. Expert Review of Pharmacoeconomics & Outcomes Research (Vol. 16, pp. 149–152). doi:10.1586/14737167.2016.1158649