In a model where subjects are evaluated over time and a baseline (
time=0) covariate is used (eg,
score ~ baseline + group + time + group*time), it seems that baseline data are often suggested to be excluded from the dependent variable (eg,
score). But excluding baseline data would seem to decrease the model accuracy.
The above model is statistically equivalent to a change from baseline analysis (eg, change from
baseline ~ baseline + group + time + group*time). If
time = 0 is not excluded, then all groups have change from baseline of 0 at time = 0, and the argument is that the 100% homogeneity at time = 0 biases the results.