Correspondence (letter to the editor): Confusing Information

Neis et al. cite findings from a randomized study on the impact of laparoscopic and laparotomy-based myomectomy on pain medication use at 72 h post-procedure (1): „85% of patients (17/20) did not require pain medication 72 hours after laparoscopic surgery compared with 15% (3/20) of patients after abdominal myomectomy (relative risk reduction [RR] 5.7; 95% confidence interval [95% CI] 2.0; 16.4)“ (1). These figures are confusing for three reasons:

First, Lethaby and Vollenhoven (2) were incorrectly cited, since they reported a relative risk (RR) (not a relative risk reduction). The RR of 5.7 is calculated by dividing 85% (no pain medication use, laparotomy group) by 15% (no pain medication use, laparoscopy group). Rather than reflecting a risk reduction, an RR of 5.7 reflects an increased risk, in this case the „risk“ (or better put: the probability) of taking no pain medication. In simple terms: the probability of not requiring further pain medication in the laparoscopy group is 5.7 times that of the laparotomy group.

Second, selecting a negative result, „not used,“ rather than a positive result, „used,“ complicates risk communication.

Third, the requirement of postoperative pain medication depends to a crucial extent on the time interval since surgery. Mais et al. reported pain medication use on postoperative day 2 (recorded between 7:00 and 11:00), whereby they called the day of surgery day 0. Thus, the percentages given by Mais et al. do not refer to „72 hours“ postoperatively, but rather 37–52 hours postoperatively (thus more like 48 hours on average), assuming that surgery was performed on day 0 between 7:00 and 18:00 (Mais et al. provided no data on the time of surgery).