· Data collected by the investigator for his own purpose is known Primary Data.
· Data collected by other person are called Secondary Data.
· The main sources of data are Primary Source of data which implies collection of data from source of origin. And the other source of data which implies that data has been collected by other.
· Main source of Secondary Data are Government Publication, Semi Government Publication.
Data published by the Railway Department regarding the progress of railway for an investigator would be treated as Secondary Data