Association of hospital and surgeon volume with mortality following major surgical procedures: Meta-analysis of meta-analyses of observational studies.

Stratification of evidence specific to an umbrella review We performed an umbrella review-level stratification of evidence using modified criteria recommended by Fusar-Poli et al [ 19 ] : Convincing evidence (Class I) when the number of cases (deaths) > 1000, highly significant summary associations (random-effects P < 10 −6 ), no evidence of small-study effects, no evidence of excess significance bias, 95% prediction intervals excluding the null, and not large heterogeneity (I 2 < 50%); Highly suggestive evidence (Class II) when the number of cases > 1000, random-effects

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Nominally significant reductions were found in odds ratio in 82% to 84% of surgical procedures in both hospital and surgeon volume-mortality associations.

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