Hi,
I am running the mlogit model and using the pwcomapre would like to compare the margins. The output specifies that "margins sharing a letter in the group label are not significantly different at the 5% level." As shown in the screenshot below, my problem is that for some items no letter is printed for my predictors in the same group. Why Stata does this?

margins i.X1##i.X2 , atmeans predict () pwcompare ( groups)
Array