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I am having trouble comparing the slopes of multiple lines. I cannot get the slope comparisons to show up in the output tables. There seems to only be a comparison of the y variable means. I select "modeling data" - "linear regression" and fill in my y and x variables then go to the "output/means" tab and select "multiple comparisons/comparison of slopes", then select "pairwise comparison" and "ok". I have 4 treatment groups and 2 time points so I'm trying to compare the slopes of all 8 lines.
In order to be able to compare the slopes, you need to include an interaction effect between the qualitative and the quantitative X variables :)
This is an ANCOVA problem.
Let us know if this still does not solve your issue.
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