Primary data is raw information collected by researchers for a specific purpose. Secondary data is information obtained by studying the reports of other researchers.
When researchers conduct primary research, they are collecting data in response to a specific question, or in accordance with a specific objective. They may conduct surveys or focus groups. They may run experiments, or record direct observations about a test subject. They may hold interviews and ask questions about the specific issues their study is designed to address. When researchers conduct secondary research, however, they do not collect any original data of their own but rely instead on the survey results, interview recordings or experimental outcomes collected by others.
There are advantages and disadvantages to both methods. The advantages of collecting primary data is that it is easy to tailor the study to a specific end. The researchers can focus only on the issues which pertain to the study. They can also control the quality of the study, and know that their findings are accurate. The disadvantage of primary research is that it is costly and time consuming. The main advantages of secondary research are that it is quick and relatively inexpensive. It is easier to examine information collected over a long period of time, and identify trends. However, the information may be outdated, or inaccurate, or too vague. Or the researcher may have to spend a great deal of time wading through data that is not pertinent.