8. Data sources for pharmacoepidemiological research
1. Data sources for pharmacoepidemiological research
Sources of pharmacoepidemiological data
There are two main approaches for data collection: collection of data specifically for a particular study or purpose (‘primary data collection’) or use of data already collected for another purpose, not aimed at research (‘secondary use of data’). Secondary data usually were once primary data but become secondary when used for a purpose different from the original one.
Primary data collection involves obtaining data de novo (i.e., new data), for example applying different study designs such as a prospective cohort study, surveys or randomised controlled trials. For some conditions, case-control surveillance networks have been developed and used for selected studies and for signal generation or clarification. Primary data in general offer increased control over the type and amount of information that is available as compared to secondary data. One of the limitations of primary data is the expenditure, labour and time involved in investigations with a progressive increase in sample size 
Secondary use of data has become the common approach in pharmacoepidemiology due to the increasing availability of electronic health records (EHR), administrative databases and other already existing data sources (see Secondary data) and due to its increased efficiency and lower cost. In addition, networking between centres active in pharmacoepidemiology and pharmacovigilance is rapidly changing (increasing) in Europe, both in terms of networks of data as well as of researchers who can contribute to a particular study with a specific data source (see Health Database networks).
In the following, brief descriptions of selected data sources in pharmacoepidemiology according to their classification are given.