Editing Stratified sampling (section)

==Sample size allocation==
For the proportional allocation strategy, the size of the sample in each stratum is taken in proportion to the size of the stratum. Suppose that in a company there are the following staff:<ref>{{cite web |last1=Hunt |first1=Neville |last2=Tyrrell |first2=Sidney |year=2001 |url=http://nestor.coventry.ac.uk/~nhunt/meths/strati.html |archive-url=https://archive.today/20131013132818/http://nestor.coventry.ac.uk/~nhunt/meths/strati.html |url-status=dead |archive-date=13 October 2013 |title=Stratified Sampling |work=Webpage at Coventry University |access-date=12 July 2012 }}</ref>
*male, full-time: 90
*male, part-time: 18
*female, full-time: 9
*female, part-time: 63
*total: 180

and we are asked to take a sample of 40 staff, stratified according to the above categories.

The first step is to calculate the percentage of each group of the total.
*% male, full-time = 90 ÷ 180 = 50%
*% male, part-time = 18 ÷ 180 = 10%
*% female, full-time = 9 ÷ 180 = 5%
*% female, part-time = 63 ÷ 180 = 35%

This tells us that of our sample of 40,
*50% (20 individuals) should be male, full-time.
*10% (4 individuals) should be male, part-time.
*5%  (2 individuals) should be female, full-time.
*35% (14 individuals) should be female, part-time.

Another easy way without having to calculate the percentage is to multiply each group size by the sample size and divide by the total population size (size of entire staff):
* male, full-time = 90 × (40 ÷ 180) = 20
* male, part-time = 18 × (40 ÷ 180) = 4
* female, full-time = 9 × (40 ÷ 180) = 2
* female, part-time = 63 × (40 ÷ 180) = 14