For some studies, e.g., in heart failure, it is traditional to normalize certain outcomes for diuretic use. For example in this paper the authors divided net fluid output by “furosemide 40mg equivalents”. In other studies the investigators might divide weight change by the same denominator. The problem as I see it is that diuretic use is adjusted over the course of observing the main response variable, so the ratio may be hard to interpret. This may be more of a situation of having a bivariate outcome: (main response variable, serial diuretic dosage). Is anyone comfortable with using the ratio as a single response variable? If we don’t do that how should concomitant therapy such as diuretic use be adjusted for?
A possibly useful background paper is here. This addresses the problem of whether linearity should be assumed for furosemide dose.