TableĀ 1

Items included in data extraction

Study characteristicsStudy findings
Study dates
Study aim
Study design
Data source and type
Study population
Unit characteristics
Definition of volume
Outcomes measured
Sample size
Number of participants
Number of events
Volume analysed as continuous or categorical variable
Volume thresholds for categorical variables
Covariates used in the analysis
Crude associations of volume and outcome
Adjusted associations of volume and outcome
Linear or non-linear relationship
Summary of main findings
Summary of limitations identified by authors