Programme: Master of Library & Information Science
Course: MLIS-09: Research Methodology
Target group: Master's students & Research Scholars
Stratified Random Sampling
When the population is heterogeneous then stratified sampling can be used to obtain more accurate results. Stratification means division of the universe into groups based on geographical, sociological or economic characteristics.
Process of Stratification
Stratified Random Sampling involves the following steps.
o
The universe is first divided into
sub-groups or strata and the required units are selected at random from each
sub-group
o
The stratification should be conducted
in such a way that the items in each group or strata should be similar to each
other but they vary significantly from items in other groups.
o
The size of each group or stratum must
be large enough so that it is possible to select the sample units using random
sampling.
o
Size of the sample from each stratum can
either be proportional or disproportional to the size of each stratum.
Merits and Demerits of Stratified Random Sampling:
This method has several advantages.
These are –
o
If the stratification is done correctly,
then even a small number of units will form a representative sample
o
In this method all the groups are
equally represented and no one group is left unrepresented
o
Bias can be controlled to a great extent
in this method. Greater accuracy can be
achieved.
o
It saves time and cost of data
collection as the sample size can be less.
The disadvantages of this method
are –
o
Dividing the population into homogeneous
groups is a difficult task
o
If the strata are overlapping or
disproportionate, then the sample may not be representative of the population
o
If the stratification is faulty then it
is not possible to correct the sampling errors.
Activity
1. The total number of staff working in a company is 180. Out of the total, 90 are Male, working full time, 18 are male working part-time; 9 females working full time; 63 are females working part-time. You want to select only 40 members from them using stratified sampling. Describe the steps and how you will select members from each group?