Chapter 13, Problem 18SE

Reading Material on Colored Paper In the past, some people believed it was easier to read words printed on colored paper than words printed on white paper, while other people believed it was easier to read words printed on white paper. To test these theories, researchers asked a sample of 15 subjects to read a passage printed in black ink twice: once on salmon-colored paper and once on white paper. The time it took to read each passage, in seconds, is given in the table. Whether the person read the salmon-colored paper first or the white paper first was determined randomly. A histogram of the differences is also shown.

a. Compare the typical values for the two groups.

b. Refer to the histogram of differences. Why is the $t$ -test potentially not appropriate for these data?

c. Carry out an appropriate hypothesis test that the typical reading time is not the same for words printed on salmon-colored paper (at least for these subjects and this passage). Use a significance level of 0.05 (with a two-sided alternative), and interpret your results.