# Mixed way ANOVA

I have two variables (group, achievement level). I want to check the effect of an intervention on different achievement levels. For example, I want to check whether there is an increase in achievement scores in low achievers, average and high achievers. Please suggest me which statistical tool should I use? Shall I use individual t-test as I have found in many articles? Or I should use mixed ANOVA?

• You say "an increase in achievement scores", do you have achievement scores from both before & after the intervention? How did you arrive at the groupings? Did you simply categorize the participants based on prior achievement scores? – gung - Reinstate Monica Apr 15 '15 at 16:16
• Yes I have both scores. I have categorized them on the basis of their summative scores. – kaushal Apr 15 '15 at 16:17

• So you want to find the average difference between groups? Its the same things, but leave out the interaction. $POST=GROUP+PRE$. Technically speaking, you can leave the interaction in there. If there is no interaction, then the models are equivalent. If there is, then that may be of interest (e.g. people responded, on average, to treatment (the main effect of GROUP), but people with low scores responded better than people with high scores(the interaction between group and pre-treatment scores)). – le_andrew Apr 15 '15 at 16:17