I have confusion about a simple statistical analysis: one dependent variable measured before and after intervention in two groups. and the classical question is comparing effects between tow groups.
consider this case: (the value of independent vaiable presneted as 1 D vector)
group 1: Pre=[200 150 100 180] -> Post =[100 75 50 90]
group 2: Pre=[20 15 10 18] -> Post =[10 7.5 5 9]
the ratio(Post/pre) of change for both groups is 50%, which means no significant effect. while difference (Post-Pre) is significantly larger in the first group.
or maybe I should use Anova. what's your solution? Could you please help me to understand this issue!