Chapter 13, Problem 17SE

The Stroop Effect Suppose you had to identify the color of ink for a series of printed words, but the printed word appeared in a color of ink that did not match the name of the color. For example, if you were shown “RED” then you should say “Blue,” but you might incorrectly say “RED” because that is what the word spells. It might take longer to correctly identify a color when it was used to print a word whose meaning did not match that color than to identify the color when the ink color and printed word matched. This difference in times is an example of something psychologists call interference and is called the Stroop effect, after research psychologist J. R. Stroop (1897-1973).

The data in the table were collected by a student conducting research on the Stroop effect. Each of 10 subjects identified colors of ink in two different situations, and the time (in seconds) was recorded. There were 36 words in each trial. In column 1, the ink was the same color as the word. In column 2, the ink and the words were different colors. Whether the subject started with the color matching the word or with the color that was different was randomly determined. Treat the data as though they came from a random sample.

a. Write a sentence comparing the median time to identify the color for the two groups. Did the task tend to take longer when the colors were different?

b. Do a sign test to test whether those who see the ink in the “wrong” color tend to take longer to identify the color. Use a significance level of 0.05.