Chapter 5 (5.5-5.7) - Internal vs. External Validity

Question 1

What does internal validity explore?

Answer 1

If the estimated causal effect is valid for the sample of observations in a given study; the answer depends on whether or not you’ve successfully eliminated all potential confounders.

Question 2

What does external validity explore?

Answer 2

If the estimated causal effect is valid beyond a given study; the answer depends on 1. if the sample of observations is representative of the population in the study and 2. if the treatment used in the study is representative of the treatment for which you want to generalize the results.

Question 3

True or false: in observational studies, you risk failing to account for all potential confounders.

Answer 3

True

Question 4

True or false: in general, studies based on randomized experiments tend to have weak internal validity, but strong external validity.

Answer 4

False

Question 5

True or false: in general, observational studies tend to have weak internal validity, but strong external validity.

Answer 5

True

Question 6

What’s the best way to ensure that a sample is representative of the population?

Answer 6

By using random sampling.

Question 7

What’s the best way to ensure that the treatment group and the control group are comparable?

Answer 7

By using random treatment assignment.

Question 8

True or false: you can rely on random treatment assignment to eliminate potential confounders.

Answer 8

False

Question 9

What does internal validity “ask”?

Answer 9

“Is the estimated causal effect valid for the sample of observations in the study?”.

Question 10

What does external validity “ask”?

Answer 10

“Is the estimated causal effect valid beyond this particular study?”.

Question 11

Regarding what internal validity “asks”, what does the answer depend on?

Answer 11

If the treatment group and the control group are comparable.

Question 12

Regarding what external validity “asks”, what does the answer depend on?

Answer 12

If the sample of observations in the study is representative of the population.

Question 13

What does randomization ensure?

Answer 13

1. that the sample is representative of the target population
2. strong external validity

Question 14

What does random treatment assignment do?

Answer 14

1. eliminates all potential confounders (making the treatment group and the control group comparable)
2. ensures strong internal validity