The major advantage of Secondary data in any research is that it is:
Helps identify gaps in the primary data and streamlines research
Provides a basis for comparison to arrive at a research finding
Sources of Secondary data can be either published or unpublished sources. Published sources include published reports of the Government, publications of foreign Government, Journals, magazines, periodicals, reports of economists, scholars, bureaus etc.
Unpublished sources include research work of teachers, scholars and professionals, records of private firms and government departments etc.