A sequence of observations, made on a set of objects included in the sample drawn from population, is known as statistical data.
(1) Ungrouped Data
Data which have been arranged in a systematic order are called raw data or ungrouped data.
(2) Grouped Data
Data presented in the form of a frequency distribution are called grouped data.
Collection of Data
The first step in any enquiry (investigation) is the collection of data. The data may be collected for the whole population or for a sample only. It is mostly collected on a sample basis. Collecting data is very difficult job. The enumerator or investigator is the well trained individual who collects the statistical data. The respondents are the persons from whom the information is collected.
Types of Data
There are two types (sources) for the collection of data:
(1) Primary Data (2) Secondary Data
(1) Primary Data
Primary data are the first hand information which is collected, compiled and published by organizations for some purpose. They are the most original data in character and have not undergone any sort of statistical treatment.
Example: Population census reports are primary data because these are collected, complied and published by the population census organization.
(2) Secondary Data
The secondary data are the second hand information which is already collected by an organization for some purpose and are available for the present study. Secondary data are not pure in character and have undergone some treatment at least once.
Example: An economic survey of England is secondary data because the data are collected by more than one organization like the Bureau of Statistics, Board of Revenue, banks, etc.
Methods of Collecting Primary Data
Primary data are collected using the following methods:
1. Personal Investigation: The researcher conducts the survey him/herself and collects data from it. The data collected in this way are usually accurate and reliable. This method of collecting data is only applicable in case of small research projects.
2. Through Investigation: Trained investigators are employed to collect the data. These investigators contact the individuals and fill in questionnaires after asking for the required information. Most organizations utilize this method.
3. Collection Through Questionnaire: Researchers get the data from local representations or agents that are based upon their own experience. This method is quick but gives only a rough estimate.
4. Through the Telephone: Researchers get information from individuals through the telephone. This method is quick and gives accurate information.
Methods of Collecting Secondary Data
Secondary data are collected by the following methods:
1. Official: e.g. publications from the Statistical Division, Ministry of Finance, the Federal Bureaus of Statistics, Ministries of Food, Agriculture, Industry, Labor, etc.
2. Semi-Official: e.g. State Bank, Railway Board, Central Cotton Committee, Boards of Economic Enquiry, etc.
3. Publication of Trade Associations, Chambers of Commerce, etc.
4. Technical and Trade Journals and Newspapers.
5. Research Organizations such as universities and other institutions.
Difference Between Primary and Secondary Data
The difference between primary and secondary data is only a change of hand. Primary data are the first hand information which is directly collected form one source. They are the most original in character and have not undergone any sort of statistical treatment, while secondary data are obtained from other sources or agencies. They are not pure in character and have undergone some treatment at least once.
Example: Suppose we are interested in finding the average age of students in a certain department. We collect the data by two methods: either by directly collecting information from each student or getting their ages from the university records. The data collected by the direct personal investigation is called primary data and the data obtained from the university records is called secondary data.
After collecting the data either from primary or secondary sources, the next step is its editing. Editing means the examination of collected data to discover any errors or mistakes before presenting it. It has to be decided beforehand what degree of accuracy is desired and what extent of errors can be tolerated in the inquiry. The editing of secondary data is simpler than that of primary data.