Concerns regarding use of one-tailed tests in the SLED-BD vs. CVVH trial

interest the recent randomized controlled trial comparing sustained low-effi ciency dialysis using a single-pass batch dialysis system (SLED-BD) with continuous veno-venous hemofi ltration (CVVH) [1]. I congratulate the authors on their undertaking but have serious concerns regarding the majority of their analysis. After each table at the end of the paper, the authors report the use of a ‘one-tailed Wilcoxon test’ to assess continuous outcomes. I do not believe this use is appropriate. As the authors themselves remark, this clinical trial represents the fi rst reasonably large trial of SLED-BD versus CVVH. Since this is the case, it is inappropriate to postulate a one-tailed hypothesis for any continuous outcomes. For example, given the available evidence, the possi bility of increased intensive care unit stay or ventilator time attributable to SLED-BD cannot be excluded. Th us, a one-tailed hypothesis is not appropriate. To convert the results reported from using a onetailed test to those using a two-tailed P value, the onetailed P value should be doubled. For example, the P value reported in Table 3 for days of mechanical ventilation (one-tailed P = 0.047) should be adjusted to a two-tailed P value of 0.094. Similarly, all other P values obtained by using a ‘one-tailed Wilcoxon test’ should also be doubled.