Secondary data is research data that has previously been gathered and can be accessed by researchers. The term contrasts with primary data, which is data collected directly from its source.
Secondary data is used to increase the sampling size of research studies and is also chosen for the efficiency and speed that comes with using an already existing resource. Secondary data facilitates large research projects, in which many research groups working in tandem collect secondary data. The main researcher is then allowed to focus on primary research or particular areas of interest. This division of labor helps researchers learn more in less time.
Common sources of existing secondary data include data collected by government public services departments, libraries, internet searches and censuses, such as the United States Census. Companies use market research to draw on existing information from social media as a source of secondary data. Social media is becoming heavily favored in market research, as opinions are already available from millions of users on many topics and products.
The benefit of using secondary data is that much of the preliminary work is done. The data may have already been sorted in an electronic format, published and reviewed with case studies already conducted. Secondary data can quickly become more or less public knowledge through use in the media. Due to its exposure and public examination, secondary data can carry more legitimacy than primary research data and is often used as verification of primary data.
However, there are a number of potential problems in using secondary data. It can be difficult to attain secondary data that the fits exact requirements of research studies. It can also be hard to verify the accuracy of secondary data, which can also become outdated over time.