I want to compare a change in 2 experimental groups to the change in 2 control groups. So I have results for one sample, then retested among another indepedent sample, and was tested among a control group, then retested among a different control. For example, the 1st experimental group had a result of 50% and the 2nd group got a 55%. The 1st control group got 60%, and the 2nd control group got 57%. So the net change is 8 ((55-50)-(57-60)). How do I determine (which stat test) if that net change is significant?