researchers examined the efficacy of 4 different treatments (a, b, c, and d) on the average change in c-reactive protein (crp) levels in a random sample of 120 adults (30 per treatment group). a crp change of 0 indicates no change in crp levels after treatment. a positive crp change ( > 0) indicates a decrease in crp levels after treatment and a negative crp change (< 0) indicates an increase in crp levels after treatment. they obtained the following results (some of the values have been hidden):