Four groups of students were subjected to different teaching techniques and tested at the end of a specified period of time. As a result of dropouts from the experimental groups (due to sickness, transfer, etc.), the number of students varied from group to group. Do the data shown in the following table present sufficient evidence to indicate a difference in mean achievement for the four teaching techniques? 1 2 3 4 65 75 94 87 69 78 89 73 83 67 80 79 81 62 88 81 72 83 69 79 76 90