Primary data are obtained by a study specifically designed to fulfil the data needs of the problems at hand. Data which are not originally collected but rather obtain from published or unpublished sources are known as secondary data.
The difference between primary and secondary data is only of degree. Data which are primary in the name of one become secondary in the hands of another.
The main sources of error in the collection of data are as follows:
- Due to direct personal interview
- Due to indirect oral interview
- Information from correspondents may be misleading.
- Mailed questionnaire may not be properly answered.
- Scheduled sent through enumerators, may give wrong information.
