Table 1.

Systematic literature review of direct evidence on the volume-outcome relationship in HD corrective surgery

	Apfeld et al. [28]	Söderström et al. [29]	Giuliani et al. [30]
Study design	retrospective analysis of hospital administrative data; multi-centre (41 centres)	retrospective analysis of hospital administrative data; single centre	retrospective analysis of hospital administrative data; multi-centre (21 centres)
Data source	Pediatric health information system (PHIS) database in the USA	Single-centre database of Stockholm University Hospital, Sweden	Hospital Episode Statistics (HES) database, UK
Follow-up time	2 years	unclear	1 year
Risk adjustment for the volume-outcome analysis (yes/no)	No	No	No
Case definition	Aggregated numbers of ostomy placement and corrective surgery	Corrective surgery	Aggregated numbers of ostomy placement, ostomy closure, biopsy, and corrective surgery
Definition of threshold	Surgeon volume: -low: < 2 procedures per year -high: >  = 2 procedures per year Hospital volume: -low: < 10 procedures per year -high: >  = 10 procedures per year	Hospital volume: -low: 7.2 corrective surgeries per year -high: 11.4 corrective surgeries per year	Hospital volume: -low: < 51 procedures per year -medium: 51–68 procedures per year -high: > 68 procedures per year
Outcomes
Mortality	–	Low-volume group: 0.9% High-volume group: 0%	Overall: 1 year mortality: 2.8% (no significant difference)
Anastomotic leak/ intestinal perforation	–	Low-volume group: 8.3% High-volume group: 3.5%	–
Cumulative length of stay within 1st year of life	–	–	Overall: 40 days (no significant difference)
Reoperation	Overall: -within 30 days: 4.5% -within 2 years: 10.2%	Low-volume group: 12.3% High-volume group: 16.9%	Overall: 11.9% (no significant difference)
Re-admission	Overall: -within 30 days: 17.2% -within 2 years: 42.6%	Low-volume group: 15.8% High-volume group: 20.5%	Overall: 41% (no significant difference)
Volume-outcome relationship for the respective outcome parameter	No	No	No

– Not applicable