Background

Small studies are prone to lower methodological quality and publication bias, and are more likely to report greater beneficial effects. A meta-epidemiological study was undertaken to investigate and quantify the impact of small study effects on meta-analyses in the neurosurgical literature.

Methods

A PubMed search was used to procure meta-analyses from Journal of Neurosurgery, Neurosurgery, Spine, Acta Neurochirurgica and Journal of Neurotrauma. Outcome data were extracted from meta-analyses the effect of study size was estimated by calculating the ratio of odds ratios (RORs) between small and large studies.

Results

16 meta-analyses of 229 primary studies and 90,629 patients were included. All but two included pooled outcomes were significantly different from 1. On average small studies did not demonstrate greater beneficial effects, with an estimated pooled ROR of 1.32 (95% CI, 0.89 to 1.75). Stratification by meta-analysis effect size and heterogeneity yielded similar findings.

Conclusions

The absence of small study effects in meta-analyses of neurosurgical studies may reflect widespread poor quality of the neurosurgical literature affecting both large and small studies, rather than an absence of publication bias.

中文翻译：

---

神经外科荟萃分析中缺乏小型研究效果：一项荟萃流行病学研究

背景

小型研究倾向于降低方法学质量和发表偏倚，并且更有可能报告更大的有益效果。进行了一项荟萃流行病学研究，以调查和量化小型研究效果对神经外科文献中荟萃分析的影响。

方法

PubMed 搜索用于从 Journal of Neurosurgery、Neurosurgery、Spine、Acta Neurochirurgica 和 Journal of Neurotrauma获取荟萃分析。从荟萃分析中提取结果数据，通过计算小型和大型研究之间的优势比 (ROR) 的比率来估计研究规模的影响。

结果

纳入 229 项初步研究和 90,629 名患者的16项荟萃分析。除两项外，所有汇总结果均与 1 显着不同。平均而言，小型研究并未显示出更大的有益效果，估计汇总 ROR 为 1.32（95% CI，0.89 至 1.75）。通过荟萃分析效应大小和异质性进行分层产生了类似的发现。

结论

神经外科研究的荟萃分析中缺乏小型研究的影响可能反映了影响大型和小型研究的神经外科文献质量普遍较差，而不是缺乏发表偏倚。