# Best model for change in scores over three time points

I have a response variable measured at three time points per individual (week 0, 18, and 36). I am interested in differences in the change of the response over the 36 weeks within some categorical variable X.

I see two ways of modeling this.

1. One way ANOVA with response = week_36_score - week_0_score (this seems like the simplest option)

2. Repeated Measures ANCOVA with response = week_18_score and week_36_score. Covariate = Week_0_score.

### Question

• Which would you prefer (if any, maybe there is a better choice)?

I know there has been a lot of articles on this and they seem to say each has its own strengths and weaknesses. I believe the second model would have more power. I am not worried about a ceiling effect here.