Weijie Cai wrote:
Hi list,
I am building a regression model with categorical predictor variable coded by treatment contrasts. The summary of the regression model shows that some levels are significant while others are not. The significant ones show that they are statistically significant from the basis factor (at level 0). How do we generally deal with those insignificant levels? If they are used for prediction, sometimes they will produce strange results because their coefficient estimates have large variances. Do we just simply ignore them assuming they are not different from level 0? Or do we exclude them in factors (by treating them as zero's) and refit the model?
any suggestions?
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