Primary and Secondary Data:

Primary Data: These data are those are collected for the first time. Thus primary data are original in character and gathered   by actual observation, measurement or enumeration. these data are called primary because they are collected from the very source from where information got generated.

Secondary Data: These data are those which have already been collected by other persons or other agency, in other words secondary data are those which have been passed through the statistical machine   at last once. These data are detached from the original source and are reprocessed by another person for his won purpose and publication.

The data which are primary in the hands of one may secondary in the hands of others. For example the census of population statistics collected by the government is primary data, if the same data are used by other investigator for his survey, will  be called secondary data .thus the statistical data which are new in the hands of investigator are primary, while  the same data use by another investigator will become secondary.