Stratified Random Sampling
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The document discusses stratified random sampling, which involves dividing a population into homogeneous subgroups called strata and randomly sampling from each stratum. It describes how to form strata based on common characteristics, how to select items from each stratum such as through systematic sampling, and how to allocate the sample size to each stratum proportionally according to the stratum's size within the overall population. An example is given of allocating a sample of 30 across 3 strata based on their relative population sizes.
Stratified Random Sampling
- 2. Presentation Compiled By : Ankita Sheth Nishant Bhrambhatt Joy Macwan
- 3. Introduction Stratified sampling technique is generally applied in order to obtain a representative sample. Under stratified sampling, the population is divided into several sub-populations that are individually more homogeneous than the population and the different sub-populations are called ‘strata’ and then we select items from each stratum to constitute a sample.
- 4. Highly Relevant Questions How to form strata? How should items be selected from each stratum? How to allocate the sample size of each stratum?
- 5. How to form strata? As we can say that strata be formed on the basis of common characteristics of the items in each stratum. Strata are usually based on past experience and personal judgment of the researcher. We can take small samples of equal size from the proposed strata and then examining the variances among the possible stratifications.
- 6. How should items be selected from each stratum? For selection of items from each stratum, Systematic Sampling can be used if it is considered more appropriate in certain situations.
- 7. How to allocate the sample size of each stratum? We usually follow the method of proportional allocation under which the sizes of the samples from the different strata are kept proportional to the sizes of the strata.
- 8. Advantages and Disadvantages
- 9. Example Let us assume that we want a sample size, n=30 to be drawn from a population of size N=8000, which is divided into 3 strata. i.e. N1=4000, N2=2400 and N3=1600. Solution: N1=4000, so 30 (4000/8000) = 15, N2=2400, so 30 (2400/8000) = 9, N3=1600, so 30 (1600/8000) = 6. So, the sample sizes for different strata are 15, 9 and 6 respectively which is in proportion to the sizes of the strata viz., 4000 : 2400 : 1600.