If a researchers in an observational study attempts to control ...

[daltonest1984]

If a researchers in an observational study attempts to control for a confounding variable, is it more likely that the resulting confidence interval will be wider or narrower than the confidence interval when he/she didn't control for the confounding variable?
 a. It will probably be wider.
  b. It will probably be narrower.
  c. It will have to be disregarded; you can't adjust or control for confounding variables after the fact.
  d. There is no way of knowing.

Question 2

Which of the following factors can make it difficult to make correct conclusions about the population based on confidence intervals?
 a. Bias in the data collection or sampling process.
  b. Confounding variables.
  c. Sample sizes that are too small to detect true differences in the population.
  d. All of the above.

[Edwyer]

Answer to Question 1

B

Answer to Question 2

D

[daltonest1984]

TYSM

[jackie]

Excellent