Your conduct secondary data analysis when you use data that someone else has gathered, usually through a survey and then computer new statistics from the data, producing a new analysis. These are many sets of secondary data that are collected specifically for this purpose and they generally have gathered a lot of information from a large, often representative, group of people. Secondary analysis is popular because it allows you to investigate research interests that would have been too expensive or time-consuming had you needed to collect the data your own.