Table 1. Description of categories of the Eindhoven Classification Model: PRISMA-medical Version [17, 18].

Main category	Subcategory	Code	Description	Examples (if available) *
Technical	External	T-ex	Technical failures beyond the control of the organisation.	Not available
	Design	TD	Failures to poor design of equipment etc.	Not available
	Construction	TC	Correct design inappropriately constructed or placed.	Not available
	Materials	TM	Material defects not classified under TD or TC.	Not available
Organisational	External	O-ex	Failures at an organisational level beyond the control and responsibility of the investigating team.	Not available
	Transfer of knowledge	OK	Failure resulting from inadequate measures to train or supervise new or inexperienced staff.	Not available
	Protocols	OP	Failures relating to the quality or availability of appropriate protocols.	• Not following pain treatment protocol after surgery
	Management priorities	OM	Internal management decisions which reduce focus on patient safety when faced with conflicting priorities.	• No beds available at ICU
	Culture	OC	Failure due to attitude and approach of the treating organisation.	• Ward where vital parameters are not frequently taken since ‘no one does it’
Human	External	H-ex	Human failures beyond the control of the organisation/department	• Intoxication of too high dosage medication prescribed outside hospital care (by GP)
	Knowledge-based behavior	HKK	Failure of an individual to apply their knowledge to a new clinical situation	• No adequate diagnostics     • No physical examination done
	Qualifications	HRQ	An inappropriately trained individual performing the clinical task	Not available
	Co-ordination	HRC	A lack of task co-ordination within the healthcare team	• No coordination of hypertension treatment
	Verification	HRV	Failure to correctly check and assess the situation before performing interventions	• DNR policy not adequately discussed
	Intervention	HRI	Failure resulting from faulty task planning or performance	• No diagnostics and adequate treatment delirium
	Monitoring	HRM	Failure to monitor the patient’s progress or condition	• No evaluation of vitals after changing treatment     • Vitals not monitored and action undertaken after reported deterioration
	Skills-based	HSS	Failure in performance of highly developed skills	• Obstructive lesion trachea not recognised/missed by radiologist on CT
Patient	Patient-related	PRF	Failures related to patient characteristics or conditions, which are beyond the control of staff and influence clinical progress	• Monitoring not adequate because patient refused CAD
	Disease-related	DRF	Failures related to the natural progress of disease which are beyond control of patient, its carers and staff	• Tumor progression in vena cava inferior     • Biliary pancreatitis
X	Unclassifiable	X		• Medication was still being dosed properly     • Toxic reaction chemotherapy

*A table with overview of all root causes is provided in S1 Table.