Sampling Methods (Jump to: Lecture | Video )

How do we select from the population what goes into our sample? Before we answer this question, we must first decide how we're going to represent different sample and population sizes.

Let’s say you want to find the average GPA of a student at your university. Your university has 20,000 students, and you select 100 students and ask them their GPAs.

What are N and n in this example?

N, the size of your population, is 20,000

n, the size of your sample, is 100

Samples are drawn from populations through several different sampling methods:

This is arguably the best sampling method, as your sampleis almost guaranteed to be representative of your population. However, it is rarely ever used due to being too impractical.

One example of this would be splitting a population of students into men and women, then sampling from each of the two groups. This may allow us to collect the same amount of information as simple random sampling, but use less people.

For example, if you add every 7th individual to walk out of a supermarket to your sample, you are performing systematic sampling.

Simply put, in this type of sampling you pick the easiest way of getting your sample. This type of sampling is sometimes called voluntary response sampling, because individuals often select to be a part of the sample. This can be a problem, because there may be a difference between people who choose to participate and people who don’t.

While there are other sampling methods not mentioned in this article, these are the most commonly used.