(i) Primary data: Those data which do not already exist in any form, and thus have to be collected for the first time from the primary source(s). By their very nature, these data are fresh and first-time collected covering the whole population or a sample drawn from it
(ii) Secondary data: They already exist in some form: published or unpublished in an identifiable secondary source. They are, generally, available from published source(s), though not necessarily in the form actually required. Eg. Data from CSO, NSSO, RBI.

1. Nominal data are the outcome of classification into two or more categories of items or units comprising a sample or a population according to some quality characteristic.
2. Classification of students according to their sex (as males and females), Workers according to their skill (as skilled, semi-skilled, and unskilled), and of employees according to their level of education (as matriculates, undergraduates, and post-graduates).

Data is the information about facts or numbers collected to be examined and used to help with decisions. Data are the basic raw materials of statistics.

1. In Medical sciences, statistical tools are widely used.
2. In order to test the efficiency of a new drug or to compare the efficiency of two drugs or two medicines, t - test for the two samples is used.
3. More and more applications of statistics are at present used in clinical investigation.

1. Statistics is necessary for the formulation of policies to start new course, according to the changing environment.
2. There are many educational institutions owned by public and private engaged in research and development work to test the past knowledge and evolve new knowledge.
3. These are possible only through statistics.