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Random sampling | Worked example

Sal Khan works through a question on random sampling from the Praxis Core Math test.

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Video transcript

- [Instructor] So we have a question here that deals with random sampling. It says the dean of students at a high school wants to ask a sample of students how they feel about the school's plan to construct a new soccer field. Which of the following methods of selecting the sample will yield the most valid information about the feelings of all the students at the school? So like always, pause this video and see if you can figure out which choice would yield the most valid information about the feelings of all the students at the school. All right, now before we even look at these choices, it's important to keep in mind that we want a sample that is random and we want to sample from the appropriate group, or an appropriate group. Sample from appropriate appropriate group. Now, let's look at the choices. Choice A says interviewing all incoming freshmen soccer players. Well that doesn't seem like it would be indicative of the feelings of all the students at the school. I would guess that the incoming freshmen soccer players would be very excited about constructing a new soccer field, but other folks might not be as excited. So this isn't, you're not selecting from a representative group right over here. Select a random sample of soccer players. Well, this has the same problem. Instead of sampling from the entire student population, you're sampling just from soccer players. Selecting a random sample of students at a soccer game. So once again, these are the students who happen to like to watch soccer games. So this wouldn't be representative of all students at the school. Selecting a random sample of all students currently enrolled at the school. Well, yes, that would be the most representative. Far more representative than either of these three choices. And then the last one, choosing three alumni who have donated the most money. Well, three alumni would not be representative of the feelings of all of the current students at the school. So I would rule that one out as well. And I would go with choice D.