In a meta-analysis of placebo controlled NSAID trials, the sensitivity of the effect variables was calculated as the correlation coefficient and as the difference between drug and placebo, divided by the placebo group standard deviation. The patient's global evaluation was the most sensitive variable overall. Pain was more sensitive than Ritchie's index. Several variables may be omitted from clinical trials, especially if two active drugs are being compared. For example, the best maximum estimate for the difference in ESR between NSAIDs and placebo was 1.0 mm/hr (95% confidence interval -1.5 to 3.4 mm/hr), and for joint size 0.44% (-1.0 to 1.9%), corresponding to a quarter of a millimeter for each of the 10 joints usually measured. It is suggested to record only the patient's global evaluation, pain, and morning stiffness.