HI

as usual with regression with interactions, the mismatching of different analyses is due to different coding of the variables. In your case, the issue is not the continuous variable (that you centered yourself so galmj, jamovi regression and R behave in the same way), but is the categorical variable (the factor centered_condition).

jamovi linear regression and default R set the reference level of the factor to one group, in your case group 0. Please notice that this does not depend on the numbers you put in the columns (i.e. -25, 0 25 is equivalent to A, B , and C, because factors are recoded internally by jamovi or R). In jamovi regression, you can go to the "Reference level" tab and change the reference group and you 'll see that the estimate of the effect of "centered_pse" will change. The same happens to in R if you do

levels(data$centered_condition)<-contr.treatment(3,base = 1)

and change base=1 to base=2 or 3. This means that the effect of "centered_pse" that you see in regression or R is the effect of centered_pse" computed for condition=0, so for that group only. It is not a main effect, it is a simple effect.

Gamlj centers the coding, so even though the comparisons made are the same as in regression and R, the coding system is centered, so you can interpret the effect of "centered_spe" as the "average effect" or the "main effect". If you want to obtain exactly the same results in gamlj and in jamovi regression, you should go to "Factor coding" in gamlj and set it to "dummy".

If you want to get in R and jamovi regression the same results than in gamlj default estimation, you need to run

levels(data$centered_condition)<-contr.treatment(3)-(1/3)

in R or set "Grand mean (simple coding)" option in jamovi regression.

Short story: All estimates are correct, they required different interpretations. R default and jamovi regression give you the simple effect of centered_pse for condition=0, gamlj gives you the main effect of it. All other coefficients are the same

Suggestion: what I guess you want to report are the main effects and interactions, so report the results of any of the following:

1) gamlj defaul

2) jamovi regression with "Grand mean (simple coding)" option on

3) R glm with levels(data$centered_condition)<-contr.treatment(3)-(1/3)

they are all equal