It is important for the investigator to decide whether to use sample or census method for collecting data. The selection primarily depends upon the nature and extent of the enquiry and the degree of accuracy desired.
Broadly speaking, there are two sources of statistical data-internal and external. Internal source refers to the information collected from within the organization. For example different organization and Government departments generate large volume of information.
In any statistical enquiry, at the outset, data are collected. Such data are to be condensed to make them fit for analysis and interpretation. Classification is the first step of condensation. There are various types of classification such as chronological, spatial, qualitative and quantitative.
Statistical data as we have seen can be either primary or secondary. Primary data are those which are collected for the first time and so are in crude form. But secondary data are those which have already been collected.
Statistics are a set of numerical data. They relate to a particular characteristic in an enquiry. Collection of these facts and figures forms the beginning of the enquiry. The person who collects the information is called the Investigator or enumerator.
According to this definition the numerical facts (data) should possess the following characteristics to be treated as statistics.
The activities of an organisation rest upon collection of factual data and information. The statistical investigator collects the primary data from the original sources and secondary data are collected from the published sources. Various methods of collection of primary data are: