i've got a stats issue that i'd love some ruling on if anyone cares to help.. i've got a population of hospital patients with a diagnosis of anemia admitted in 2004 - n=191 the rate at which these 191 catch the flu while in stay is 39% (or 75 of them) during that same time (2004) 90 of these anemia patients were given a special drug. these 90 pats caught the flu while in stay at a rate of 23% (or 21 of them) now, my contention is that i can only say that there was a 16% improvement related to the taking of the special drug (or 39%-23% = 16%) a friend of mine says that there is a 41% improvement because of the "percent change in" method (or 39%-23% = 16% then 16%/39% = 41%) i say you cannot do this since it is not the same population that has changed, and there is not two time periods over which you are measuring change i.e. town x's # of crimes in 2003 was 75, in 2004 it was 21, thus town x's crime rate has had a 72% (not 41%) reduction from 2003 to 2004 (or (75-21)/75 = .72) any help would be appreciated, thanks in advance. edit to say: i titled this "stats question" even though i know that for anyone with a working knowledge of statistical analysis this is extremely simple. danke!