I already used lots of search engines without finding an answer to my problem.

I am testing two methods for manipulating religious belief. For each of the methods there exists an experimental and a control group. So there are in total four groups (between-subject design).

My hypothesis is the following:

Exp1 - Contr1 > Exp2 - Contr2

How do I test if one of the differences is bigger than the other? The interaction between the factors "Exp. vs. Contr." and "method of manipulation" is significant.

Thanks in advance.

Cheers,

Konstantin