Secondary data are second hand informations. They are not collected from the source as the primary data. In other words, secondary data are those which have already been collected. So they may be relatively less accurate than the primary data. Secondary data are generally used when the time of enquiry is short and the accuracy of the enquiry can be compromised to some extent. Secondary data can be collected from a number of sources which can broadly be classified into two categories.
i) Published sources
ii) Unpublished sources
Mostly secondary data are collected from published sources. Some important sources of published data are the following.
1. Published reports of Central and State Governments and local bodies.
2. Statistical abstracts, census reports and other reports published by different ministries of the Government.
3. Official publications of the foreign Governments.
4. Reports and Publications of trade associations, chambers of commerce, financial institutions etc.
5. Journals, Magazines and periodicals.
6. Periodic Publications of Government organizations like Central Statistical Organization (C. S. O.), National Sample Survey Organization (NSSO).
7. Reports submitted by Economists, Research Scholars, Bureaus etc.
8. Published works of research institutions and Universities etc.
Statistical data can also be collected from various unpublished sources. Some of the important unpublished sources from which secondary data can be collected are:
1. The research works carried out by scholars, teachers and professionals.
2. The records maintained by private firms and business enterprises. They may not like to publish the information considering them as business secret.
3. Records and statistics maintained by various departments and offices of the Central and State Governments, Corporations, Undertakings etc.
Secondary data are already collected informations. They might have been collected for some specific purposes. So they must be used with caution. It is generally very different to verify such information to find out inconsistencies, errors, omissions etc. Therefore scrutiny of secondary data is essential. Because the data might be inaccurate, unsuitable or inadequate. Thus it is very risky to use statistics collected by other people unless they have been thoroughly edited and found reliable, adequate and suitable for the purpose.