group 7-- Cluster Vs Stratified ---> Shanika Jhunjhunwala

Shanika Jhunjhunwala
2013040

Cluster sampling-

In this mode of sampling, the naturally occurring groups are selected for being included in the sample. Its main use is in market research. In this method, the total population is divided into samples or groups after which, a sample of the groups is selected. After this process, relevant and required data from all the elements of all the groups is collected. At times, instead of collecting information from each group, information can be collected from a sub-sample of the elements. If the variation is between the members of the groups and not between the actual groups, then this technique will work the best. The clusters are collectively exhaustive and mutually exclusive.

Stratified Sampling-

In this technique, a sample is divided into stratum and on random basis. Different stratums are created which will allow the usage of different sampling percentage in each stratum. These stratums are nothing but simple groups which consists of a number of elements. On these stratums, simple random selection is performed. Every element is assigned only one stratum. This method is known to produce weighted mean whose variability is less than that of arithmetic mean of a simple random sample of the population. In stratified sampling also, the strata should be collectively exhaustive and mutually exclusive. This will help in applying random or systematic sampling in each of the stratum. This will also help in the reduction of errors.

Cluster Vs Stratified:

Cluster Sampling-

• When natural groupings are evident in a statistical population, this technique is used.
•  It can be opted if the group consists of homogeneous members.
•  Its advantages are that it is cheaper as compared to the other methods.
• The main disadvantage is that it introduces higher errors.

Stratified Sampling-

• In this method, the members are grouped into relatively homogeneous groups.
• It is a good option for heterogeneous members.
• The advantages are that this method ignores the irrelevant ones and focuses on the crucial sub populations.
• Another advantage is that for different sub populations, you can opt for different techniques. This also helps in improving the efficiency and accuracy of the estimation.
• The disadvantages are that it requires choice of relevant stratification variables which can be tough at times. When there are homogeneous subgroups, it is not much useful. Its implementation is expensive. If not provided with accurate information about the population, then an error may be introduced.

Cluster sampling and stratified sampling are two different sampling methods. The main difference between them is that a cluster is treated as sampling unit. Hence in the first stage, analysis is done on a population of clusters. While, in stratified sampling, the elements within the strata are analyzed.