[Freesurfer] reporting bhvat value from lme

Dear Freesurfers

We are now finishing an article, where we have used linear mixed models included in FreeSurfer 5.3 for longitudinal changes between two-time points. We have used this model. Intercept(RF) + centered time+ group + group*centered time + sex(gender).

Everything is clear except for one thing. When we used this contrast vector [0 1 0 1 0] to get longitudinal change for the study group, we get two bhvat values. How can we calculate these two bhvat values to one bhvat vaule in position two and four? Should we just add them together after we have been multiple them with the contrast vector, or add them as sqrt(a^2+b^2)?

Best regards Knut Jørgen Bjuland NTNU