All people in sampling frame are divided into groups or categories called strata. Within each group, a simple random sample or systematic sample is selected. I have decided to do a simple random sample. Example of stratified sampling:
If I want to ensure that a sample of 10 students from a group of 100 contains both male and female students in same proportions as in the full population, first divide that population into male and female. In this example, there are 54 male students and 46 females. To work out the number of males and females in the sample i will need to do the following calculations: No. of males in sample = (10/100) x 54 = 5.4
No. of females in sample = (10/100) x 46 = 4.6
I obviously can't have.4 of a person or .6 of a person in my sample, and so have to "round" the numbers. Therefore i would choose 5 males and 5 females in the sample. I will then use the random sampling technique to get my sample. I will put the females and males in seperate groups, and number them in order. I will then use the random number generator on my calculator and which ever number comes up multiply it by the size of the population and then i will use the corresponding person from the group. I will do this until i have the amount of each that i had worked out earlier using my stratified sampling method.
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