Table 1

Characteristics of included studies, ordered by year of publication

Study	Year	Country	Data source	Primary diagnosis or clinical procedure	Quality indicator(s)	Level(s) at which variation is analysed	Quality rating*
Selby et al 21	2010	USA	Administrative	Hypertension Hyperlipaemia Primary care visits Women age 52–69 years	Systolic BP LDL-cholesterol Care experience score Screening mammography	Hospital Physician	Good
Osler et al 31	2011	Denmark	Clinical registry	Colon cancer surgery	30-day mortality	Hospital	Good
Elferink et al 25	2011	Netherlands	Clinical registry	Colon cancer surgery	Number of LN assessed	Hospital Pathologist	Good
Nathan et al 15	2011	USA	Administrative	Colon cancer surgery	≥12 LN assessment	Hospital Physician Pathologist	Good
Cooke et al 32	2012	USA	Health records	Non-surgical mechanically ventilated patients	30-day mortality	Hospital	Good
Seymour et al 33	2012	USA	Administrative	Hospitalised AMI patients, pneumonia, CHF, CRC surgery	ICU use	Hospital	Good
Goodwin et al 22	2013	USA	Administrative	Inpatient population	Length of stay, 30-day mortality, % discharged home, % discharged to SNF, 30-day ER visit, 30-day readmission	Hospital Physician Patient	Good
Koné Péfoyo and Wodchis19	2013	Canada	Survey	Acute inpatient population	Rating nurses and doctors, patient-centred care, admission process, communication, discharge transition, pain management	Hospital	Good
Baines et al 34	2013	Netherlands	Health records	Inpatient population	AE, preventable AE	Hospital	Good
Gathara et al 26	2015	Kenia	Survey	Malaria, pneumonia, diarrhoea and underage inpatient population	Dose prescription (quinine, zinc, crystalline penicillin), HIV testing	Hospital	Fair
Prescott et al 35	2015	USA	Administrative	First hospitalisation involving severe sepsis	30-day mortality	Hospital Region	Good
van de Vijsel et al 36	2015	Netherlands	Clinical registry	AMI, CVA, CHF, cholecystectomy, hip fracture, THA, TKA, pneumonia, colon cancer	Length of stay	Hospital	Good
Pozo-Rodríguez et al 37	2015	Spain	Clinical registry	COPD exacerbations	In-hospital mortality, 90-day mortality, readmission	Hospital	Fair
Ghith et al 30	2016	Sweden	Administrative	Primary diagnosis of heart failure	30-day mortality	Hospital Ward	Good
El-Sheikha38	2016	England	Survey	Varicose veins treatment	Change in AVVQ	Hospital	Fair
Guillouët et al 17	2016	France	Clinical registry	Peritoneal dialysis	Early PD failure	Hospital	Good
Admon et al 14	2017	USA	Administrative	CHF, AMI, AIS, COPD, pneumonia, hip fracture (treated with arthroplasty)	ICU admission status	Hospital	Good
Orindi et al 39	2017	7 EU countries	Survey	Inpatient population	Patient satisfaction with care	Hospital Country Nursing unit	Fair
Charalampopoulos et al 40	2017	England, Wales	Clinical registry	Type 1 DM	Glycaemic control (HbA1c)	Clinic	Good
Korda et al 18	2017	Australia	Survey	CHF	30-day readmission 30-day mortality	Hospital	Good
Bottle et al 20	2018	England	Administrative	THA and TKA	All-cause 30-day readmission, surgical 30-day readmission and 30-day readmission with RTT	Hospital Physician	Good
Hekkert et al 41	2018	Netherlands	Administrative	Biliary tract disease, OA, hip fracture, cardiac dysrhythmia, appendicitis, urinary tract calculus, hernia, device complications, prostatic hyperplasia, surgical complications	All cause 30-day readmission	Hospital	Good
Charalampopoulos et al 42	2018	8 high income countries	Clinical registry	Children with type 1 DM	Glycaemic control (HbA1c)	Clinic	Good
Gutacker et al 1	2018	England	Clinical registry	AMI, CABG, pneumonia, hip fracture, THA, AIS	28-day readmission 30-day mortality Length of stay	Hospital Physician	Good
Berlin et al 43	2019	USA	Survey	Breast cancer surgery (breast reconstruction)	Complications, satisfaction with aesthetics and outcome	Hospital	Good
Kristensen et al 44	2019	Denmark	Clinical registry	Hip fracture treated surgically	All cause 30-day mortality	Hospital	Good
Comendeiro-Maaløe et al 27	2020	5 EU countries	Administrative	AMI+subgroup CHF	In-hospital mortality	Hospital	Good
Kristensen et al 45	2020	Sweden	Administrative	Hip fracture	1 year all-cause mortality	Municipality Hospital	Good
Khor et al 23	2020	USA	Survey	Lumbar fusion procedure	MID improvement in ODI at 12 months, % reaching minimal disability	Hospital Physician	Good
Rodriguez-Lopez et al 28	2020	Sweden	Clinical registry	AMI	30-day mortality	Hospital Patient	Good
Wang et al 46	2020	USA	Administrative	Pancreatic cancer surgery	30-day readmission	Hospital	Good
Jackson et al 47	2020	USA	Clinical registry	HLA-incompatible living donor kidney transplantation	Mortality Graft loss	Hospital	Good
Liu et al 48	2021	China	Clinical registry	Type 2 DM	Length of stay	Hospital	Good
Vesterager et al 49	2021	Denmark	Clinical registry	Hip fracture surgery	Hospital-treated infections Pneumonia Sepsis Community-treated infections	Hospital	Good
Bamdad et al 24	2022	USA	Clinical registry	Elective colectomy	Non-UTI postoperative complications (within 30 days after surgery)	Hospital Physician	Good
Bernet et al 50	2022	Switzerland	Survey	Acute inpatient population	Inpatient fall rate	Hospital	Good
Bottle et al 51	2022	England	Administrative	COVID-19	In-hospital mortality	Hospital	Good
Ferreira et al 52	2022	Australia	Health records	ED presentations of patients with low back pain	Hospital adjusted admission rate	Hospital	Good
Stankovic et al 53	2022	Denmark	Clinical registry	Cardiac arrest	ROSC 1-year survival 30-day survival	Hospital	Good
Salet et al 10	2022	Netherlands	Administrative	Laparoscopic resection of CRC, urinary bladder carcinoma resection, acute PCI, TKA for OA	In-hospital mortality, ICU admission, length of stay, 30-day readmission, 30-day reintervention	Hospital Physician	Good
Chui et al 16	2023	USA	Administrative	Patients eligible for CRT-D	CRT-D utilisation	Hospital	Good
Liu et al 54	2023	China	Survey	Cancer care in tertiary hospitals	Patient experience of; administrative process, hospital environment, medical care, symptom management, overall satisfaction	Hospital	Good
Bakhtiyar et al 55	2023	USA	Clinical registry	Kidney transplantation	Length of stay	Hospital	Good
Estupiñán-Romero et al 56	2023	Spain	Administrative	AIS (yes/no undergoing reperfusion therapy)	30-day in-hospital mortality	Hospital	Good

*According to risk-of-bias assessment using the National Institute of Health quality assessment tool for observational cohort and cross-sectional studies.
AE, adverse event; AIS, acute ischaemic stroke; AMI, acute myocardial infarction; AVVQ, Aberdeen Varicose Vein Score Questionnaire; BP, blood pressure; CABG, isolated coronary artery bypass graft surgery; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; CRC, colorectal carcinoma; CRT-D, cardiac resynchronisation therapy-defibrillator; CVA, cerebrovascular accident; DM, diabetes mellitus; ED, emegency department; ER, emergency room; EU, European Union; HbA1c, haemoglobin A1c/glycated haemoglobin; HLA, human leukocyte antigens ; ICU, intensive care unit; LDL, low-density lipoprotein; LN, lymph node; MID, minimal important difference; OA, osteoarthritis; ODI, Oswestry low back pain Disability Index; PCI, percutaneous coronary intervention; PD, peritoneal dialysis; ROSC, return of spontaneous circulation; RTT, return-to-theatre; SNF, skilled nursing facility; THA, total hip arthroplasty; TKA, total knee arthroplasty; UTI, urinary tract infection.