I\'m having difficulty understanding when to use certain studies/ what they are.

Question

I'm having difficulty understanding when to use certain studies/ what they are. Could you please explain! Thanks!

Ex. Question:

A teacher would like to know whether test A or test B is more difficult for students. She selected 80 students, 40 of whom were randomly selected for test A and the other 40 for test B. The average grade on test A was 85 with a standard deviation of 10, and the average grade on test B was 80 with a standard deviation of 15 points. This is an example of what type of study?

a) Observational study

b) Matched pairs designed experiment

c) Two-group completely random design

d) Stratified design

Explanation / Answer

Answer: c) Two-group completely random design

Observational study is where the independent variable is not under the control of the researcher. Here the independent variable is the two types of test and it is under the control of the researcher or the teacher(randomly assigns students to each test).

Matched pairs designed experiment involves the same group exposed to multiple treatments. Here a set of students is assigned to test A, but a different set of students is assigned to test B, therefore this is not a matched pairs designed experiment

Stratification is the process of dividing members of the population into subgroups before sampling. Here, it is a random assignment of students to different tests.

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