by **mcfanda@gmail.com** » Tue May 18, 2021 6:56 am

Hi,

if you have two conditions, the F-test of the interaction between your IV (independent variables) is the test you're looking for. The interaction test null hypothesis is that the simple slopes are all equal, so if the test is significant, you can say that the simple slopes are not all equal. In the case of two conditions, this means that the two simple slopes are different.

If you have more than two conditions, saying that the simple slopes are not all equal does not mean that they are all different. Thus, you need to look at the interaction coefficients, in the "Parameter Estimates" table. For instance, if your conditions are 1,2,3, and the continuous IV is called X, the interaction coefficient labelled "1-2 * X" informs you on whether the simple slope of X is different between condition 1 and 2, whereas the interaction coefficient "1-3 * X" informs you on whether the simple slope of X is different between condition 1 and 3.