19. Suppose that at a state college, a random sample of 41 students is drawn, and each of the 41 students in the sample is asked to measure the length of their right foot in centimeters. A 95% confidence interval for the mean foot length for students at this college turns out to be (21.709, 25.091). If instead a 90% confidence interval was calculated, how would it differ from the 95% confidence interval?

(A) The 90% confidence interval would be narrower.

(B) The 90% confidence interval would be wider.

(C) The 90% confidence interval would be the same as the 95% confidence interval.

20. From the previous question, consider the 95% confidence interval for the mean foot length for students at this college, which turned out to be (21.709, 25.091). What does a 95% confidence interval for mean foot length tell us in this case? Select the best answer:

(A) We are 95% confident that this interval contains the sample mean (X) foot length.

(B) About 95% of the state college students will have a foot length within this interval.

(C) We are 95% confident that most state college students will have foot lengths within this interval.

(D) If this experiment were repeated independently many times, about 95% of the confidence intervals obtained would contain the population mean foot length. The next three items refer to the following situation: A research article reports the results of a new drug test. The drug is to be used to decrease vision loss in people with Macular Degeneration. The article gives a P-value of .04 in the analysis section.

The next three items present three different interpretations of this P-value. Indicate whether each interpretation is valid or invalid.

21. The P-value can be interpreted as the probability of getting results as extreme as or more extreme than the ones in this study if the drug is actually not effective.

(A) Valid (B) Invalid

22. The P-value can be interpreted as the probability that the drug is not effective.

(A) Valid (B) Invalid

23. The P-value can be interpreted as the probability that the drug is effective

(A) Valid (B) Invalid

24. Suppose a researcher is hoping to show that the results of an experiment are statistically significant. In the statistical analysis, which of the following P-values would the researcher prefer?

(A) .01

(B) .1

(C) 1.0

(D) P-values are not related to statistical significance.