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.
Primary data are always collected from the source. It is collected either by the investigator himself or through his agents. There are different methods of collecting primary data. Each method has its relative merits and demerits. The investigator has to choose a particular method to collect the information. The choice to a large extent depends on the preliminaries to data collection some of the commonly used methods are discussed below.
1. Direct Personal observation:
This is a very general method of collecting primary data. Here the investigator directly contacts the informants, solicits their cooperation and enumerates the data. The information are collected by direct personal interviews.
The novelty of this method is its simplicity. It is neither difficult for the enumerator nor the informants. Because both are present at the spot of data collection. This method provides most accurate information as the investigator collects them personally. But as the investigator alone is involved in the process, his personal bias may influence the accuracy of the data. So it is necessary that the investigator should be honest, unbiased and experienced. In such cases the data collected may be fairly accurate. However, the method is quite costly and time-consuming. So the method should be used when the scope of enquiry is small.
2. Indirect Oral Interviews :
This is an indirect method of collecting primary data. Here information are not collected directly from the source but by interviewing persons closely related with the problem. This method is applied to apprehend culprits in case of theft, murder etc. The informations relating to one’s personal life or which the informant hesitates to reveal are better collected by this method. Here the investigator prepares ‘a small list of questions relating to the enquiry. The answers (information) are collected by interviewing persons well connected with the incident. The investigator should cross-examine the informants to get correct information.
This method is time saving and involves relatively less cost. The accuracy of the information largely depends upon the integrity of the investigator. It is desirable that the investigator should be experienced and capable enough to inspire and create confidence in the informant to collect accurate data.
3. Mailed Questionnaire method:
This is a very commonly used method of collecting primary data. Here information are collected through a set of questionnaire. A questionnaire is a document prepared by the investigator containing a set of questions. These questions relate to the problem of enquiry directly or indirectly. Here first the questionnaires are mailed to the informants with a formal request to answer the question and send them back. For better response the investigator should bear the postal charges. The questionnaire should carry a polite note explaining the aims and objective of the enquiry, definition of various terms and concepts used there. Besides this the investigator should ensure the secrecy of the information as well as the name of the informants, if required.
Success of this method greatly depends upon the way in which the questionnaire is drafted. So the investigator must be very careful while framing the questions. The questions should be
(i) Short and clear
(ii) Few in number
(iii) Simple and intelligible
(iv) Corroboratory in nature or there should be provision for cross check
(v) Impersonal, non-aggressive type
(vi) Simple alternative, multiple-choice or open-end type
(a) In the simple alternative question type, the respondent has to choose between alternatives such as ‘Yes or No’, ‘right or wrong’ etc.
For example: Is Adam Smith called father of Statistics ? Yes/No,
(b) In the multiple choice type, the respondent has to answer from any of the given alternatives.
Example: To which sector do you belong ?
(i) Primary Sector
(ii) Secondary Sector
(iii) Tertiary or Service Sector
(c) In the Open-end or free answer questions the respondents are given complete freedom in answering the questions. The questions are like –
What are the defects of our educational system ?
The questionnaire method is very economical in terms of time, energy and money. The method is widely used when the scope of enquiry is large. Data collected by this method are not affected by the personal bias of the investigator. However the accuracy of the information depends on the cooperation and honesty of the informants. This method can be used only if the informants are cooperative, conscious and educated. This limits the scope of the method.
4. Schedule Method:
In case the informants are largely uneducated and non-responsive data cannot be collected by the mailed questionnaire method. In such cases, schedule method is used to collect data. Here the questionnaires are sent through the enumerators to collect informations. Enumerators are persons appointed by the investigator for the purpose. They directly meet the informants with the questionnaire. They explain the scope and objective of the enquiry to the informants and solicit their cooperation. The enumerators ask the questions to the informants and record their answers in the questionnaire and compile them. The success of this method depends on the sincerity and efficiency of the enumerators. So the enumerator should be sweet-tempered, good-natured, trained and well-behaved.
Schedule method is widely used in extensive studies. It gives fairly correct result as the enumerators directly collect the information. The accuracy of the information depends upon the honesty of the enumerators. They should be unbiased. This method is relatively more costly and time-consuming than the mailed questionnaire method.
5. From Local Agents:
Sometimes primary data are collected from local agents or correspondents. These agents are appointed by the sponsoring authorities. They are well conversant with the local conditions like language, communication, food habits, traditions etc. Being on the spot and well acquainted with the nature of the enquiry they are capable of furnishing reliable information.
The accuracy of the data collected by this method depends on the honesty and sincerity of the agents. Because they actually collect the information from the spot. Information from a wide area at less cost and time can be collected by this method. The method is generally used by government agencies, newspapers, periodicals etc. to collect data.
Information are like raw materials or inputs in an enquiry. The result of the enquiry basically depends on the type of information used. Primary data can be collected by employing any of the above methods. The investigator should make a rational choice of the methods to be used for collecting data. Because collection of data forms the beginning of the statistical enquiry.