Methods of Sampling
The various methods of sampling may be grouped under two categories, namely, Random sampling method and Non-random sampling method. They are briefly explained as follows.
1. Random Sampling methods
In the case of random sampling, every unit of the population has equal chance of getting selected. It is not so in the case of non-random sampling. Random sampling method can be divided into Simple Random Sampling and Restricted Random Sampling.
1. Simple Random Sampling
In this method, the personal bias of the researcher does not influence the sample selection. Chance factor alone will decide the selection of the sample.
2. Restricted Random Sampling
There are three methods of restricted random sampling each of which is briefly explained below:
a. Stratified Sampling
Here, the population units are divided into different strata (social class) and a specific number of units is selected from each stratum at random. For example, a marketer of a particular brand of detergent soap may want to study the number of buyers buying his product in the city of Chennai. If he wants to use stratified sampling, he may have to divide the buyers into different categories according to their monthly income. He will then select from each category at random a particular number of persons.
b. Systematic Sampling
In this method, the selection of the random sample is done in a systematic manner. For example, if the researcher wants to study the monthly expenditure of households in a particular locality and wants to use the systematic sample selection approach, he may choose, for example, every 5th house in each street in that locality (1st, 5th, 10th, 15th, 20th, and so on).
c. Cluster Sampling
A ‘cluster’ is nothing but a group. In the case of cluster sampling, the selection of samples at random is done at various stages. For example, a marketer may want to study the effectiveness of. advertising in a particular city. If he wants to use the cluster sampling approach, he will first divide the city into different localities and then select certain localities at random. From the localities selected, he will select the streets at random. From the streets selected, he will select the households at random.
2. Non-Random Sampling Methods
Non-Random Sampling can be divided into Judgement Sampling, Convenience Sampling and Quota Sampling as detailed below.
In this method, the selection of sample is done by the researcher according to his judgement. For example, if a manufacturer wants to study the performance of the dealers of his product in a State, and fixes the sample size at 50, he may select any 50 dealers who in his opinion represent the total number of dealers in the State.
In this case, the researcher selects the sample according to his convenience. For example, a marketer who wants to study the behavior of buyers on the basis of a sample study may pick up the sample from the nearby market.
Here, sample is selected according to a quota system. For example, in a study on the impact of television advertisement, if the researcher has fixed the sample size at 100, he may contact 30 housewives, 20 working women, 30 men and 20 college students.