About Sample Design

What do you mean by “Sample Design”? What points should be taken into consideration by a researcher in developing a sample design for his research project?

Introduction:

A sample design is a definite plan for obtaining a sample from a given population.  It refers to the technique or the procedure the researcher would adopt in selecting items for the sample.  Sample design may as well lay down the number of items to be included in the sample in the size of the sample.  Sample design is determined before data are collected.  There are many sample designs from which a researcher can choose.  Some designs are relatively more precise is easier to apply than others.  Researcher must select / prepare a sample design, which should be reliable and appropriate for his research study.

The following points should be taken into consideration by a researcher while developing a sample design

Type of Universe.

Sampling Unit.

Source Unit.

Size of sample.

Parameters of interest.

Budgetary constraints.

Sampling procedure.

Type of Universe: The first step in developing any samples design is to clearly define the set of objects, technically called the universe.  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 the city, the number of workers in a factory and the like are examples of finite universes, were as the number of stars in the sky, listeners of a specific radio programme, throwing of a dice etc., are examples of infinite universes.

Sampling Unit: A decision has to be taken concerning a sampling unit before selecting sample.  Sampling unit may be 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.

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 finite universe only).  If source list is not available, researcher has to prepare it.  Such a list should be comprehensive correct, reliable is appropriate.  It is extremely important for the source list to be as representative of the population.

Size of Sample: The size of the sample should neither be excessively large nor too small.  It should be optimum.  An optimum sample is one which fulfills the requirements of efficiency, reprsentativeness, reliability and flexibility, while deciding the size of sample, researcher must determine the desired precision as also an acceptable confidence level for the estimate.  The size of the population variance needs to be considered as in case of larger variance usually a bigger sample is needed.  The size of the population variance usually a bigger sample is needed.  The size of population must be kept in view for this also limits the sample size.  The parameters of interest in a research study must be kept in view, while deciding the size of the sample.  The budgetary constraint must invariably be taken into consideration when we decide the sample size.

Parameters of Interest: In determining the sample design, one must consider the question of the specific population parameters which are of interest from 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 considerations from practical point of view, have a major impact upon decisions relating to not only the size of the sample but also to be type of sample.  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 of the sample.  This technique or procidure stands for the sample design itself.  There are several sample designs out of which the researcher must choose one of his study.  Obviously, he must select that design which, for a given sample size is for a given cost, has a smaller sampling error.