What are the types of Purposive Sampling method as used in Statistics?

What are the types of Purposive Sampling method as used in Statistics?

Types of Purposive Sampling

Following are the main types of purposive sampling.

A. Quota Sampling:

It is a type of purposive sampling in which the whole universe is divided first into certain parts and the total sample is allocated among these parts! Each part of’ the population is assigned to an investigator for whom the quota of the units to be examined by him is fixed in advance according to certain specified characteristics such as sex, age, occupation, income group, political or religious affiliation.

The invigilator is asked to select the required number of units of the sample of his own accord and examine them to get the desired information as quickly as possible.

He is also authorized to substitute the new units in the quota if he finds that any unit of the sample so selected is not responding up to the mark. This method is very often used in opinion poll surveys, market surveys and political surveys.

Example

Suppose we make a public opinion survey of “New Budget of Govt, of’ India-2003” In quota sampling, interviewers are asked to interview a total 1000 persons of the area allotted.

It has also been asked that out of each 100 persons 80 are housewives, 30 are farmers, 30 are industrialists, 20 are transporters and 20 are fixed salary persons. In this way, each category will have its quota. In our example, housewives’ 400, of farmers 200, industrialists 200, transporters 100, and the fixed salary persons 100.

Merits

(i) Purposive Sampling:

It enjoys all the advantages of purposive or judgment sampling.

(ii) Reliable Results:

It gives more reliable and dependable results, if the investigators are skilled the experienced and their works are properly supervised.

(iii) Economical:

There is considerable saving in time and money as the sampled units may be so selected that they are close together.

Demerits

(i) It suffers from all the defects of a purposive sampling.

(ii) Scope of Mischief:

The investigator is free to play mischief in the selection of the items of the sample and collection of the data.

(iii) Not Possible to Estimate Sample error:

It is not possible to estimate the sampling error and the degree of accuracy achieved.

B. Convenience Sampling

It is a type of purposive sampling in which the sample units are selected purposively by the investigator to suit his convenience in the matter of location and contract with the units.

This method of selecting the sample is also called ‘Chunk’ since the samples under this method are selected neither on the basis of the rules of probability nor on the basis of the judgment of the investigator but on the basis of convenience on the part of the investigator.

For example, a sample obtained from a list of students in a college for enquiring into their educational problems, is a matter of convenience sampling as in such a case it will be convenient for the investigator to locate and contract the selected students for obtaining the desired information from them.

Example

Suppose we have to study the problems faced by Sugar Industry in Uttar Pradesh. Now, if we choose 20 units which are in our easy command, sampling technique will be termed as convenience sampling.

Merits

(i) Easy Command:

The units of the sample are easily located and contacted by the investigators.

(ii) Economical:

It is less expensive and less time consuming.

(iii) Suitable for Pilot Surveys:

It is suitable for making pilot surveys in which questions are pre-tested and preliminary information’s are obtained before finalizing the sample design.

Demerits

(i) Does not represent Universe:

The units of the sample selected under this method hardly represent the universe.

(ii) Bias:

It is very much influenced by the bias and personal convenience of the investigator.

(iii) Unsatisfactory Results:

The results obtained under this method are found to be unsatisfactory and misleading.

(iv) Personal convenience of Investigator:

It is based neither on the rules of probability nor on the principle of judgment but on the personal convenience of the investigator.