Samples: Representative, Random & Biased

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  • 0:01 Different Kinds of Samples
  • 0:46 Representative Samples
  • 1:55 Random Samples
  • 2:50 Biased Samples
  • 3:45 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

When conducting statistical research, a great deal of importance hinges on the type of sample you use. In this lesson, we will learn about representative, random, and biased samples, as well as which is best for what situation.

Different Kinds of Samples

Let's say that you wanted to run a survey. One of the most important things that you could do to guarantee that your survey is taken seriously is to guarantee that the sample is reliable. The sample is the group chosen to be asked questions in your survey.

In the past, you may have surveyed classmates about their opinions on something. Chances are that your class was small enough to ask just about everyone how they felt. However, your class is a relatively small group. Imagine having to find out how your whole state felt, or even the entire country? Needless to say, you'd probably find it much better just to ask a small group that represents the others - in other words, a sample.

Representative Samples

The best samples are almost always representative samples. Representative samples match up to your population in very general ways. For example, if your class had 20 girls and 10 boys, then a representative sample size would include twice as many girls as boys. Of course, when people take surveys, they have to account for much more than if someone is male or female. Statisticians call these allowances for specific ratios of people within the study a way of making sure that the study is controlled.

Controls refer to the steps that survey takers go through to make sure that only the questions that they ask are up for debate. For example, pretend that you were asking a bunch of people how they felt about your favorite football team's new coach. It would only really make sense to ask people who have an opinion about your football team. Also, if you were only considering the opinions of the teams' fans, it only makes sense to ask other fans. They are likely to have a different opinion than someone who cheers for your team's big rival.

Random Samples

Sometimes it is impossible to get truly representative samples. Think about how hard it would be to get a representative sample of a group that you didn't know anything about! Where would you even start? In that case, random samples are best. Random samples are just that; they are completely random. In these instances, the survey takers put everyone's information in a big database and use a computer program that chooses a certain number of people at random.

Imagine that you were asking people in a big city what their favorite pizza place was for a news story. Now, you could feasibly conduct a fully representative study, but that would take time away from writing the story. Worse yet, that could be expensive if you had to track down every possible way that a person could be representative. It's much better to just take a random sample from people across the city.

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