We read with interest the recent meta-analysis by Yu et al. [1] comparing biportal endoscopic spine surgery (BESS) with conventional open techniques. The authors are to be commended for synthesizing evidence in this rapidly evolving field. Nevertheless, we would like to highlight a significant numerical inconsistency in the reported standardized effect sizes for operative time, which, unless clarified, may compromise the reliability of the study’s primary conclusion.

The manuscript reports pooled descriptive statistics of 101.34±41.91 minutes (open) and 134.57±80.75 minutes (BESS), alongside a pooled standardized effect size of d=2.19 (95% confidence interval [CI], 0.75–3.64; p=0.003) [1]. By the conventional formula for Cohen’s d (mean difference divided by pooled standard deviation) [2–4], the pooled standard deviation (SD) of these groups is: pooled SD=√((41.91²+80.75²)/2)≈64.33.

The observed mean difference is 134.57–101.34=33.23 minutes, yielding Cohen’s d≈0.52, not 2.19. A value of d=2.19 would correspond to an operative-time difference of approximately 141 minutes, which is incompatible with the reported group means. Similarly, in the fusion subgroup, the reported means (129.25±24.87 minutes vs. 186.69±63.83 minutes) imply an observed difference of 57.44 minutes and a pooled SD≈48.44, giving d≈1.19, rather than the stated 2.57 [1]. These discrepancies suggest an error in calculation, transcription, or labeling of the effect sizes.

Accurate computation of standardized mean differences is essential, as they are conceptually distinct from inferential statistics and directly influence the interpretation of pooled results [2,3,5]. Misestimation of effect sizes of this magnitude may overstate clinical differences and misinform subsequent evidence syntheses. Established methodological guidance emphasizes precise calculation and transparent reporting [2,4,5].

In light of these findings, we would recommend that the authors (1) provide a transparent extraction table including per-study means, standard deviations, and sample sizes used for the operative-time analysis; (2) disclose the analytic workflow (e.g., RevMan file, R syntax, or equivalent) to ensure reproducibility; and (3) recalculate the pooled effect size, preferably reporting the raw mean difference in minutes with 95% CIs, as this metric is more interpretable when all studies share the same unit of measurement.

Such revisions would not only enable independent verification but also enhance the methodological rigor, clinical applicability, and credibility of the review’s conclusions.

Thank you for considering this clarification. We hope these comments will support constructive dialogue and strengthen the evidence base on this important topic.