A movie studio executive wants to determine which of four potential trailers for a new film will be most likely to result affect ticket sales. One of the trailers features comedic scenes, another features dramatic scenes, a third features scary scenes, and the last features action scenes. The exec puts together a small focus group in which the members view all of the trailers and rate the effectiveness of each, using a 9-point scale (from not at all to extremely). Source of Variation SS df MS F Within-subjects 3 21.875 Between persons 3 Within groups (error) 12.590 Total 103.210 15