Video engineers use time compression to shorten the time required for broadcasting a television commercial. But can shorter commercials be effective? To answer this question, 200 college students were randomly divided into three groups. The first group (57 students) was shown a videotape of a television program that included a 30-second commercial; the second group (74 students) was shown the same videotape but with the 24-second time-compressed version of the commercial; and the third group (69 students) was shown a 20- second time-compressed version of the commercial. Two days after viewing the tape, the three groups of students were asked to name the brand that was advertised. The numbers of students recalling the brand name for each of the three groups are given in the table below.

a. Do the data provide sufficient evidence (at α = .05) that the two directions of classification, type of commercial and recall of brand name, are dependent? Interpret your results.

b. Construct a 95% confidence interval for the difference between the proportions recalling brand name for viewers of normal and 24-second time-compressed commercials.