> When I run 2 sessions at a time, I do get similar beta coefficients, but I get a slightly bigger
> T-Stat than if I run each run individually. Do you know why that is?
The reason is that with the two runs combined, you double the number of data points to estimate the residuals (noise), leading to slightly more precise and smaller standard error for each effect estimate.
For your question, you should not use parentheses when setting up a general linear test. However, it's not clear to me what is your utmost goal. Why are you doing conjunction analysis?
Gang