# Pretest scores differ amongst groups

In my analysis I compare 3 treatment groups with a pre- and posttest (emotionality scores 0 - 100), so I want to use the repeated measures. Unfortunately, the pretest scores differ significantly amoungst groups which makes me think that simply running the test would not be valid. When I transfer the scores to relative ones, I get uninterpretable data due to the method of measurement (0 = not emotional, 100 = very emotional): a baseline score of 40 and postscore of 80 should not be interpreted as equal to a baseline score of 2 and a postscore of 4.

Any ideas on how to tackle this problem?

• Was this a randomized experiment? If no, e.g. stratifying the analysis by propensity score may be an option. – Björn Jan 13 '16 at 12:27
• It was a randomized experiment indeed. – Guest with a question Jan 13 '16 at 12:45

$Y = X \beta + \epsilon$
$Y = X \beta + Z \gamma + \epsilon$