True about cluster sampling are all except
|A||Sample size is same as that of simple random sampling|
|B||It is a two stage sampling|
|C||It is cheaper than other methods of sampling|
|D||It has the disadvantage of higher sampling error|
Ref: Basic & Clinical Biostatistics; Dawson – Saunders & Trapp
- The sample size is never the same as that of simple random sampling in cluster sampling.
- In fact the sample size in cluster is twice or thrice that of SRS because of the phenomenon of Design Effect.
- The very reason for carrying out cluster sampling is for administrative & operational feasibility. In this method, instead of selecting individuals, a subset of clusters or groups are randomly selected and then all respondents or a pre-determined number of respondents in each cluster are included in the study.
- The result is considered to be statistically valid within the error limit of 10%. However the method is definitely less efficient to simple random sampling & requires a larger sample size, but in some situations it is the method of choice, such as in multicentric trials, in order to obtain adequate number of patients.
- Cluster sampling is most frequently used in immunization coverage evaluation surveys.