This sounds very dumb actually. But I tried to control for treatment type (T1, T2, and T3) in the regression results below, and all of them are omitted due to collinearity. Actually, there are four treatment types: T1, T2, T3, and CONTROL. I left out CONTROL as a base for comparison.

Having said that, is there a way to figure out why this is happening? I know this is difficult without actually looking at the data though.

Thanks!


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