SYSTEMATIC SAMPLING – Systematic sampling is an easier procedure than random sampling when you have a large population and the names of the targeted population are available. Systematic sampling involves selection of every nth (i.e., 5th) subject in the population to be in the sample.
Suppose you had a list of 10,000 voters in your school district and you wished to sample 400 voters to see if they supported special funding for a new school program.
We divide the number in the population (10,000) by the size of the sample we wish to use (400) and we get the interval we need to use when selecting subjects (25). In order to select 400 subjects, we need to select every 25 person on the list.
Before we start selecting subjects, we need to select a random starting point on the list. That starting point must be with one of the first 25 names on the list. We would use a random number table to determine the starting point. Once we have the starting point, we select that subject and every 25th subject after that on the list.
Population Size / Desired Sample Size = Interval