In practice, most statistical data exist in official and private records that are compiled as part of the routine of the day-to-day activities of public organizations and private firms. Thus, government departments routinely record figures on such matters as births and deaths, number of accidents, per period, quantities of items exported or imported per period etc. Private firms also maintain continuous records on personnel, sales, expenses, production, etc.
Primary data are those which are collected for the first time and thus original in character, whereas secondary data are those which have already been collected by some other persons and which have passed through the statistical machine at least once. Primary data are in the shape of raw materials to which statistical methods are applied for the purpose of analysis and interpretations. Secondary data are usually in the shape of finished products since they have been treated statistically in some form or the other. Therefore when
data are used for purposes other than those for which they were originally complied, they are known as ‘secondary’ data.
It may be observed that the distinction between primary and secondary data is a matter of degree or relativity only. The same set of data may be secondary in the hands of one and primary in the hands of others. In general, the data are primary to the source who collects and processes them for the first time and are secondary for all other sources who later use such data. For instance, the data relating to mortality (death rates) and fertility (birth rate) in Kenya published by the office of Registrar of births and deaths are primary whereas the same reproduced by the United Nations Organization (U.N.O) in its United Nations Statistical Abstract
become secondary in as far as the later agency (UNO) is concerned.
Choice between Primary and Secondary Data
Obviously, there are a lot of differences in the method of collection of primary and secondary data. In the case of primary data which is to be collected originally, the entire scheme of the plan starting with the definition of various terms used, units to be employed, type of enquiry to be conducted, extent of accuracy aimed at etc, is to be formulated whereas the collection of secondary data is in the form of mere compilation of the existing data.
A proper choice between the types of data needed for any particular statistical investigation is to be made after taking into consideration:
- that nature
- the objective, and
- scope of the enquiry;
- the time and finances (budget) at the disposal of researcher;
- The degree of precision aimed at; when conducting a survey, primary data on the great advantage in that the exact information is obtained. Terms can be carefully defined so that misunderstandings are avoided as far as is possible. In fact the investigations can be geared to cover all the ground considered necessary without having to rely on possibly out of date information. The staff carrying out the investigation can be specifically picked for the purpose in mind.Many business statistics are compiled from secondary data which has certain advantages.
- The information will be obtained more speedily, and at less cost than primary data.
- In addition, no large army of investigators will be required.
Secondary data must, however be used with great care, and the investigator must be satisfied that the data is sufficiently accurate for statistical investigation. It is necessary for the researcher to know the source, the method of compilation and the purpose for which the original investigation was carried out.
Furthermore, information must be available as to the units in which the data is expressed including any change in those units since their original collection, and the degree of accuracy of the results cannot be determined. Secondary data provides an important source of statistical information, particularly when circumstances make it impractical to obtain primary data. It must always, however, be applied in full knowledge of its limitations.