Hi. This tutorial will cover convenience and self-selected samples.
Let's start with some motivation. Suppose you're interested in learning about whether or not people in your neighborhood are planning to move in the next six months. A representative sample would be needed since a census would be impractical. Recall that a census is when you survey an entire population. Since we're assuming that our neighborhood is relatively large, it would be impractical to do a census. So we would need a sample instead.
To select your sample, you may be tempted to ask several of your direct neighbors. This method of sampling, called convenience sampling, is bad. And here's why.
Suppose your block of neighbors consists of primarily renters rather than homeowners. Since renters are generally more mobile, this sample would likely result in a high proportion of neighbors interested in moving. Convenience samples are not representative samples.
So a convenience sample is a sample selected using an easily available or convenient group. Now based on that-- now that we have a definition of convenience sample, we can also look at what's called a self-selected sample, and that is a sample that relies entirely on individuals who volunteer to be part of the sample. Keyword here volunteer. So this will consist of generally all volunteers.
Common studies that use self-selected samples involve internet surveys, mail-back surveys, and call in surveys. Generally, individuals who volunteer for the study have a strong interest in the research question. Using only these individuals in a sample will give data that is not representative of the entire population. Chances are you're going to get the people that really favor whatever you're measuring or strongly oppose whatever you're measuring. You're generally not going to get a lot of middle ground in these self-selected samples.
So really guys, the key idea that we need to cover here is convenience sampling is bad because it does not produce a representative sample. Thanks for watching and we'll see you soon.