In my analysis, I have 4 groups:
FLU-P (symptoms with virus)
FLU-N (symptoms without virus)
HCY-P (healthy with virus)
HCY-N (healthy without virus)
I am looking at the level of antibody (dichotomous: normal/ deficient) in these 4 groups....so I ran a Chi-square test (FLU-P vs FLU-N vs HCY-P vs HCY-N).
But I would like to do further comparisons, such as:
FLU-P & FLU-N vs HCY-N or
FLU-N vs HCY-P & HCY-N,
my 2 questions are: 1. am I allow to regroup groups & omit group like what I have just described in an analysis? 2. is chi-square still the right test to use? if not, any suggestion?