This lesson will explain two types of samples: convenience and self-selected samples, including:
One of the things that we know about sampling is that it's important for samples to be representative of the population. What we mean by that is when we take our sample, which is a subset of a larger population, we want this sample to behave just like the population would if we sampled them all. Now, sampling everybody is not a sample at all; that’s called a census.
We want the sample to behave as similar to the population as possible, so that when we calculate statistics from our data, the statistics are as accurate about the population as they can be. Make sense?
The sample should represent the group/population at large, so it’s important individuals are selected carefully for the sample. That way, accurate information will be gained and can be used to describe the group/population at large.
The goal is to generalize what is found in the “sample” box and apply it to the people outside of the box, labeled above as the “population”.
The two methods analyzed in this tutorial have major flaws-- these two designs do not result in representative samples. They are conducted often, so it’s important for you to recognize them.
Suppose there is a crowd of people at a mall and there is one guy with a clipboard, and he wants some data. He might take the people nearest to him, and say, “Hey, would you like to take my survey please?”
The people he asks might be representative of the population, but they might not. They all happen to be at the same place at the same time.
This means they might have some similarities that could make them not representative of the larger population. The risk of them not representing the group/population at large is too high.
Convenience sampling is not valid because people in similar locations often feel the same way.
If you ask people about their spending habits, and they are shopping in the headphones section, that probably means they have similar ideas about how they should spend their money.
There's also self-selected samples. We also call them voluntary response samples. And those are samples where people can choose to participate. Focus groups is a common example of self-selected samples.
Participants who feel very strongly about the subject at hand are likely to be the volunteer for the self-selected sample. On the other end of the spectrum, participants may be compensated for the time and the participants simply tell the interviewer what they want to hear.
If your focus group is about politics, you might get only the very, very liberal people or the very, very conservative people. And then there's a lot of people who are ambivalent about politics. They don't really care, but they want to get paid if this is a sample that offers compensation or another type of reward like free lunch. You'll get the most extreme viewpoints and none of the viewpoints in the middle.
Representative samples are important if we want to generalize our findings to the population, which is exactly what we want to do. Convenience samples render people who are simply in the vicinity and happen to be at the same place at the same time. Self-selected samples are also called “voluntary response” and tend to elicit either strong opinions or no opinion at all.
Source: this work is adapted from sophia author jonathan osters.
A sample that is easily obtained. It is often not representative of the population.
A sample that accurately reflects the population.
A sample that the participants choose to be a part of.