# The result of absolute change and relative change in t test is different

My task is to evaluate the effectiveness of an intervention. In my study, there are one control group and one intervention group. There are two time points, baseline and endpoint. And I use the score of some questionnaire as outcome measures.

My strategy to show/test the effectiveness is to compare the change between baseline and endpoint between these two groups by independent t test for continuous measures.

I calculated both the point difference $(\text{endpoint}-\text{baseline})$ and relative difference $((\text{endpoint}-\text{baseline})/\text{baseline})$. After running t test in SPSS, I got two different result that the $p$-value of the $t$-test on point difference was higher than $0.05$ and $p$-value of the $t$-test on relative difference is lower than $0.05$.

These results were contradicting because I set the alpha as $0.05$.

I want to ask: which difference should I use?