I often need to get the CI for the ratio of means for bioequivalence testing. I know using a log transformation on the data and then converting back the associated CIs accomplishes this. The problem I have is the data contains negative values (% change in lesion counts). I have tried adding a constant, but the resulting CIs change depending on the constant I use. I am using the following code to convert the CI of the difference of the treatment means into a CI for the ratio of means: *getconfidence interval for difference of treatment means; odslisting close; odsoutput lsmeandiffcl=cla(rename=(dependent=_name_)); procglm data=pp(where=(extrt ne 'Vehicle')); class extrt siteid; model pchinf=extrt siteid; lsmeans extrt/out=lsm alpha=0.10stderr pdiff cl; *get lsmeans for treatment; run; quit; odslisting; dataequci&outvar; merge cla lsm(where=(extrt='Reference'));*usereference lsmean for denominator; by _name_; length ciles $30; *reverse sign because above CI calculatedon reference-test difference instead of test-reference difference; ciles='('||cats(put((-uppercl/lsmean)+1,5.3))||','||cats(put((-lowercl/lsmean)+1,5.3))||')^{super1}'; run; I believe the method is sound, but I am unable to find any kind of documentation to back it up. Any comments? Craig
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