# How can I analyze changes over time between two groups?

I have data from two groups - let's call them Group A and Group B. - from three different time points. Data are collected on day 1, day 50, and day 100. I collected writing errors at each of those time points. Both groups were reacting to an intervention and both produced errors which I categorized. The problem is that the number of participants varied across time points. So I collected the total numbers of errors so that I can compare general trends.

What I am trying to understand is how to analyze this data. I'm not sure how to interpret the changes beyond a very simple descriptive analysis along the lines of "Group B showed a larger decrease than Group A for Error Type 2".

These numbers refer to the % of errors by category. For example, on Day 1 the Type 2 Errors made by Group A were 22.45% of the total errors they made. Whereas on Day 100, the Type 2 Errors made by Group A had fallen to 6.45% of the total errors they made on Day 100.

Any advice on ways to analyze this data would be greatly appreciated. Even advice on simple qualitative analysis would be great.