IBM Corporation has been retraining many of its employees to assume marketing positions. As part of this effort, the company wanted to test four possible methods of training marketing personnel to determine if at least one of the methods was better than the others. Four groups of 70 employees each were assigned to the four training methods. The employees were pretested for marketing ability and put into groups of four, each group constituting a block with approximately equal prior ability. Then the four employees in each group were randomly assigned to the four training methods and retested after completion of the three-week training session. The differences between their initial scores and final scores were computed. The results were analyzed using a block design ANOVA. The results of the analysis include: SSTR = 9,875, SSBL = 1,445 and SST = 22,364. Are all four training methods equally effective? Explain.