8.

Researchers randomly assigned college students to drink either water or two cans of Red Bull. Immediately afterwards, all students completed the GRE. The researchers concluded that Red Bull had essentially no effect on GRE scores. Which result matches this conclusion?

d_unbiased = 0.01, 95% CI [0.02, 0.04]

d_unbiased= 1.0, 95% CI [0.8, 1.2]

d_unbiased= -1.0, 95% CI [1.2, 0.8]

d_unbiased= 0.01, 95% CI [2.0, 2.0]

9.

A researcher randomly assigns participants to either an exercise group or a sleep group before taking a motor-skills test. She uses the NHST approach, with a null hypothesis thatM_sleep- M_exercise= 0 and an of 0.05. She reports:t(38) = 3.02,p= 0.004. Which of the following is the best answer?

The researcher will fail to reject the null hypothesis.

The likelihood of Type I error is high.

This is a statistically significant finding.

The 95% CI for M_sleep- M_exercisewill include 0.

10.

For the same study described in the previous question, imagine that the researcher had not randomly assigned participants to sleep or exercise. Instead, imagine that she recruited participants and split them into two groups based on whether or not, in the hour before the study, they happened to have slept or exercised. What would be different about this approach?

Without random assignment, no confidence interval can be calculated.

Without random assignment, the NHST approach cannot be used.

Because sleep and exercise are measured differently, it would be necessary to use d.

Without random assignment, the researcher cannot draw causal conclusions.