Suppose that four groups, each consisting of 100 randomly selected individuals, were exposed to four different commercials about Tide detergent. After seeing the commercial, each individual provided ratings on preference for Tide, preference for Proctor and Gamble (the company making Tide), and preference for the commercial itself. Because these three preference dependent variables are correlated, should be conducted to determine which commercial is the most effective (produced the highest preferences across the three variables).