Practical Example
In general the size of the sample in each stratum is taken in proportion to the size of the stratum. This is called proportional allocation. Suppose that in a company there are the following staff:
- 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 find the total number of staff (180) and calculate the percentage in each group.
- % 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% should be male, full-time.
- 10% should be male, part-time.
- 5% should be female, full-time.
- 35% should be female, part-time.
- 50% of 40 is 20.
- 10% of 40 is 4.
- 5% of 40 is 2.
- 35% of 40 is 14.
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 x (40 / 180) = 20
- male, part-time = 18 x (40 / 180) = 4
- female, full-time = 9 x (40 / 180) = 2
- female, part-time = 63 x (40 / 180) = 14
Read more about this topic: Stratified Sampling
Famous quotes containing the word practical:
“I do not remember anything which Confucius has said directly respecting man’s “origin, purpose, and destiny.” He was more practical than that. He is full of wisdom applied to human relations,—to the private life,—the family,—government, etc. It is remarkable that, according to his own account, the sum and substance of his teaching is, as you know, to do as you would be done by.”
—Henry David Thoreau (1817–1862)
“War-making is one of the few activities that people are not supposed to view “realistically”; that is, with an eye to expense and practical outcome. In all-out war, expenditure is all-out, unprudent—war being defined as an emergency in which no sacrifice is excessive.”
—Susan Sontag (b. 1933)