Sampling in Research:
In research studies, a sample is a a group of people, objects, or items that are taken from a larger population for measurement. The sample in question should represent the population to ensure that the researcher can generalize the findings from the research sample to the population as a whole.
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Sampling in research studies
Sample Design in Research:
- A sample design is a definite plan for obtaining a sample from a given population for research purposes.
- It refers to the technique or the procedure the researcher would adopt in selecting the sample size.
- Sample design is determined before data are collected.
- There are many sample designs from which a researcher can choose.
Elements of Sample Design in Research:
While developing a sampling design, the researcher must pay attention to the following points:
- Type of universe: The first step in developing any sample design is to clearly define the set of objects, technically called the Universe, to be studied. The universe can be finite or infinite. In finite universe the number of items is certain, but in case of an infinite universe the number of items is infinite, i.e., we cannot have any idea about the total number of items. The population of a city, the number of workers in a factory and the like are examples of finite universes, whereas the number of stars in the sky is an example of infinite universe.
- Sampling unit: A decision has to be taken concerning a sampling unit before selecting sample. Sampling unit may be a geographical one such as state, district, village, etc., or a construction unit such as house, flat, etc., or it may be a social unit such as family, club, school, etc., or it may be an individual. The researcher will have to decide one or more of such units that he has to select for his study.
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- Source list: It is also known as „sampling frame‟ from which sample is to be drawn. It contains the names of all items of a universe (in case of finite universe only).
- Size of sample: This refers to the number of items to be selected from the universe to constitute a sample. This a major problem before a researcher. The size of sample should neither be excessively large, nor too small. It should be optimum.
- Parameters of interest: In determining the sample design, one must consider the question of the specific population parameters which are of interest. For instance, we may be interested in estimating the proportion of persons with some characteristic in the population, or we may be interested in knowing some average or the other measure concerning the population. There may also be important sub-groups in the population about whom we would like to make estimates. All this has a strong impact upon the sample design we would accept.
- Budgetary constraint: Cost is an important factor for designing a sample size. Because, larger sample size involves more money. This fact can even lead to the use of a non-probability sample.
- Sampling procedure: Finally, the researcher must decide the type of sample he will use i.e., he must decide about the technique to be used in selecting the items for the sample. Obviously, he must select that design which, for a given sample size and for a given cost, has a smaller sampling error.