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Dispersion on the other hand is about, as in above case, whether majority of students have scored marks near the average or far away from the average. For example average of 1 and -1 is 0. Similarly average of 100 and -100 is also 0. In the first case data values are near the average i.e dispersion is less while in the second case data values are more scattered or spread or away from the average i.e dispersion is more. The most common measure of dispersion is the standard deviation

2.2 Methods of collection of primary data*

Primary data is data collected for the first time through census or
sample. There are several ways of collecting such data. These are:

– Direct personal interview or observation.
– Indirect personal interview or observation.
– Mailed questionnaire.
– Schedules through enumerators.

In the direct personal interview, the investigator collects the information directly from the sources concerned. For example, an investigator may collect information about cost of cultivation through personal interaction with the farmers who cultivate the land.


– Information so collected is more accurate, reliable and useful. The investigator can check and countercheck the information and get in the form in which he desires.
– The investigator can put alternative questions suited to the educational and cultural level of the persons concerned.
– In such cases, information can be collected by eliminating the bias and prejudices of the persons concerned.


– Such a method can be adopted only when the enquiry is intensive and localized to a locality or a group. This cannot be used when the enquiry is extensive or is to be done in large areas.

– Such an enquiry is subjective in the sense that the intelligence, tact, skill as well as personal bias of the investigator are all reflected in the process

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