Is this an SRS? A large nation
Is this an SRS? A large national telecommunications company hasabout 20,000 non-management employees and 3,000 managementemployees. A survey of employee opinion about recent changes inhealth care coverage selects 400 of the non-management employees atrandom and 60 of the management employees at random. The 460employees make up the sample. a) Does this sampling method giveeach employee an equal chance to be chosen? Why or why not? b) Isthis an SRS? Why or why not?
Answer:
(a)
There are 20000 non-management employees and 400 wereselected.
So, probability of a non-management employee to be selected =400/20000 = 1/50
There are 3000 non-management employees and 60 wereselected.
So, probability of a non-management employee to be selected =60/3000 = 1/50
Clearly, the method gives each employee an equalchance to be chosen.
(b)
We know, SRS stands for SimpleRandom Sampling. While we use this sampling procedure, we choosesample from the whole population data set in each draw (with orwithout replacement).
So, this is not SRS.
This sampling procedure observedhere is StratifiedRandom Sampling. In stratified random sampling, we dividethe whole population into homogeneous strata of similar kind andthen perform Simple Random Sampling (with or without replacement)in each strata to get sample and finally add all samples from allstrata to get sample set.
Here also, whole population wasdivided into two homogeneous strata as management andnon-management employees and simple random samples were drawn fromboth strata to obtain sample and finally all selected employeesmake up the sample.
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