Sampling 3

Sampling 3 Sasmita Mishra

Non-Probability Sampling  It

does not afford any basis for estimating the probability that each element in the population has equal chance of being included in the sample  It is mainly based upon the judgment of the researcher

Purposive Sampling  

It is also called ‘deliberate sampling’ or ‘judgment sampling’. Here the researcher deliberately selects certain units for study from the universe According to Adolph Jenson, “purposive selection denotes the method of selecting a number of groups of units in such a way that the selected groups together yield as nearly as possible the same averages or proportion as the totality with respect to these characteristics which are already a matter of statistical knowledge.

Merits of Purposive Sampling 

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Under proper controls and safeguards this method can prove very useful. It is more economical and less time-consuming. This method ensures proper representation of a cross-section of various strata of the universe if the researcher has full knowledge of the composition of the universe. This method is very useful specially when some of the units are very important and their inclusion in the study is necessary. It is a practical method where randomization is not possible

Demerits of Purposive Sampling 

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Under this method prior knowledge of the universe is necessary which in most cases is not possible Controls and safeguards adopted under this method are sometimes not effective and there is very possibility of the selection of biased samples Under this method the calculation of sample errors is not possible.

Quota Sampling  It

is a special type of stratified sampling  Under this method population is stratified on some basis, preferably on the basis of the characteristics of the population under study. After this the number of sample units to be selected from each stratum is decided by the researcher in advance.

Merits of Quota Sampling 

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It is a stratified-cum-purposive sampling and thus enjoys both above named method. It is a practical and convenient method. If proper controls or checks are imposed on the investigator, quota sampling is likely to give accurate results. It is only useful method when no sample frame is available.

Demerits of Quota Sampling 

This method suffers from the limitations of both stratified and purposive sampling

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Control over field work is a very difficult task. Hence, the result may be biased because of the personal beliefs and prejudices of the investigator in the selection of the units under study

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Since quota sampling is not based on random sampling, the sampling error as well as standard error cannot be estimated.

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Since the samples are not randomly selected, they may not be technically true representative of the universe.

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The bias may also occur due to substitution of unlike sample units.

Convenience Sampling    

It is known as unsystematic, careless, accidental or opportunistic sampling Under this method a sample is selected according to the convenience of the investigator. This convenience may be in respect of availability of data,accessibility of the units etc. This method may be used in the following cases: 1. When the universe is not clearly defined 2. When sampling unit is not clear 3. When a complete source list is not available