The statistical analyses of the study "Sufentanil Sublingual Tablet System (SSTS) for the management of postoperative pain after major abdominal and gynecological surgery within an ERAS protocol: an observational study"[Letter].

Dear editor

We read the observational study “Sufentanil Sublingual Tablet System (SSTS) for the management of postoperative pain after major abdominal and gynecological surgery within an ERAS protocol: an observational study” of Stefano Turi et al.1 published in August 2019, Volume 12, p2313–2319 with great pleasure. I think that the findings detected in this study will contribute to the clinical practice. However, the statistical analyses were not appropriate.

In the "Data analysis" section, the authors stated that

"Pain intensity was calculated as the mean NRS value at first administration (baseline, V0), and during the following 24, 48, and 72 hrs (V1, V2, and V3, respectively). Pain intensity at different timepoints was compared using the Student’s t-test".

The effect of time should be considered by the authors to measure the NRS value at each pre-determined assessment time. Therefore, we think the pain intensity at different timepoints should be analyzed using a repeated-measures analysis.