So there is only one change? or 4?
If 4 is it always 1 week after?
Example:
Control: 50, 50, 50, 50, 50, 50, 50, 50,
Group1: 50, 40, 40, 40, 30, 30, 30, 30
Group2: 50, 50, 40, 40, 40, 30, 30, 30
If so, do you expect to get the same result on Group1 week2 (n) and group2 week3 (n+1)?
What do you compare between the groups?