Collection of data in statistics :
We may define ‘data’ as quantitative information about some particular characteristic(s) under consideration.
Although a distinction can be made between a qualitative characteristic and a quantitative characteristic but so far as the statistical analysis of the characteristic is concerned, we need to convert qualitative information to quantitative information by providing a numeric descriptions to the given characteristic.
In this connection, we may note that a quantitative characteristic is known as a variable or in other words, a variable is a measurable quantity.
Again, a variable may be either discrete or continuous.
Discrete variable :
When a variable assumes a finite or a countably infinite number of isolated values, it is known as a discrete variable.
Examples of discrete variables may be found in the number of petals in a flower, the number of misprints a
book contains, the number of road accidents in a particular locality and so on.
Continuous variable :
A variable, on the other hand, is known to be continuous if it can assume any value from a given interval.
Examples of continuous variables may be provided by height, weight, sale, profit and so on.
Finally, a qualitative characteristic is known as an attribute. The gender of a baby, the nationality of a person, the color of a flower etc. are examples of attributes.
Collection of data plays the very important role for any statistical analysis.
The data which are collected for the first time by an investigator or agency are known as primary data whereas the data are known to be secondary if the data, as being already collected, are used by a different person or agency.
Thus, if Prof. David collects the data on the height of every student in his class,then these would be primary data for him. If, however, another person, say, Professor Daniel uses the data, as collected by Prof. David, for finding the average height of the students belonging to that class, then the data would be secondary for Prof. Daniel.
The following methods are employed for the collection of primary data:
(i) Interview method
(ii) Mailed questionnaire method
(iii) Observation method
(iv) Questionnaires filled and sent by enumerators
Interview method :
Interview method again could be divided into
(a) Personal Interview method
(b) Indirect Interview method
(c) Telephone Interview method.
In personal interview method, the investigator meets the respondents directly and collects the required information then and there from them.
In case of a natural calamity like a super cyclone or an earthquake or an epidemic like plague, we may collect the necessary data much more quickly and accurately by applying this method.
If there are some practical problems in reaching the respondents directly, as in the case of a rail accident, then we may take recourse for conducting Indirect Interview where the investigator collects the necessary information from the persons associated with the problems.
Telephone interview method is a quick and rather non-expensive way to collect the primary data where the relevant information can be gathered by the researcher himself by contacting the interviewee over the phone.
The first two methods, though more accurate, are inapplicable for covering a large area whereas the telephone interview, though less consistent, has a wide
coverage. The amount of non-responses is maximum for this third method of data collection.
Mailed questionnaire method :
Mailed questionnaire method comprises of framing a well-drafted and soundly-sequenced questionnaire covering all the important aspects of the problem under consideration and sending them to the respondents with pre-paid stamp after providing all the necessary guidelines for filling up the questionnaire.
Although a wide area can be covered using the mailed questionnaire method, the amount of non-responses is likely to be maximum in this method.
Observation method :
In observation method, data are collected, as in the case of obtaining the data on the height and weight of a group of students, by direct observation or using instrument. Although this is likely to be the best method for data collection, it is time consuming, laborious and covers only a small area.
Questionnaires filled and sent by enumerators :
Questionnaire form of data collection is used for larger inquiries from the persons who are surveyed. Enumerators collects information directly by interviewing the persons having information : Question are explained and hence data is collected.
There are many sources of getting secondary data. Some important sources are listed below :
(a) International sources like WHO, ILO, IMF, World Bank etc.
(b) Government sources, such as the U.S. Census Bureau.
(c) Corporate filings, such as annual reports to the U.S. Securities and Exchange Commission (SEC)
(d) Trade, business and professional associations.
(e) Media, including broadcast, print and Internet.
(h) Unpublished sources of various research institutes, researchers etc.
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