There are some agencies both at the national and state level to collect, process and tabulate the statistical data. Some of these at the national level are Census of India, National Sample Survey Organisation (NSSO), Central Statistical Office (CSO), Labour Bureau etc.
(i) Census of India provides most complete and continuous demographic record of population. Since 1881, it is being conducted regularly every ten years. The first Census after independence was conducted in 1951. Census data is interpreted and analysed to understand many economic and social issues in India.
(ii) National Sample Survey Organisation (NSSO) established by the Government of India to conduct nationwide survey, on socio-economic issues. The data collected by NSSO are released through reports and its quarterly journal 'Sarvekshana'.
(a) Throw light on the agency at the national level providing most complete and continuous demographic record of the population.
(b )Which quarterly journal is released by the NSSO?

The data based on first hand information are called 'Primary Data', as they are based on first-hand data. On the other hand, if the data have been collected and processed by some other agency, they are called 'Secondary Data' which can be obtained either from published sources such as government reports, documents, newspapers, websites etc. or from unpublished sources. Thus, the data are primary to the source that collects and processes them for the first time and secondary for all sources that later use such data. Use of secondary data saves time and cost.
(a) Give any two examples of published sources of data.
(b) 'Secondary data of today was primary data of yester years.' Elaborate.