Table 1.

Definitions, descriptions and examples of the error types described in the amplified version of GEMS [4,5]

	Error type	Definition	Example from previous work [4]
			Description of error	Evidence from scenario (S) or debrief (D)
Original GEMS categorisations	Skill-based slips and lapses	“errors which result from some failure in the execution [slip] and/or storage [lapse] stage of an action sequence” [5]	Patient’s notes not checked for current medications as possible cause of hypoglycaemic coma	Junior (D): “I completely forgot about the kardex [drug chart], that’s when I was going to read that he was diabetic, and then the phone went”
	Rule-based mistakes (RBMs)	“the mistake arises from the application of a ‘bad’ rule or the misapplication of a ‘good’ rule [a rule of proven worth]” [5]	Juniors aware that senior help is not arriving for 20 minutes and patient having a major post-operative bleed	Tutor (D): “Did 2222 [emergency call] cross your mind?” Junior: “Yes it did at one point.” Tutor: “Why didn”t you call it?“ Junior: ”I felt like the patient’s consciousness wasn’t impaired.”
	Knowledge-based mistakes (KBMs)	Mistakes arising from “the more laborious mode of making inferences from knowledge-based mental models of the problem space” [5]	Recognition of partial airway obstruction but no simple manoeuvres attempted and no advice sought	Junior (S): “He’s sounding very obstructed; he’s got an obstructed airway.” Reply from other junior: “We can’t do anything about it, can we?”
	Violations	“Deliberate deviations from those practices deemed necessary to maintain the safe operation of a potentially hazardous system” [5]	Feels patient’s pulse but does not count rate or ask for any monitoring	Junior (S): “He’s got a pulse as well; I can’t tell the rate, I don’t have a watch.”
Novel error types	Compound errors	Errors occurring solely because of a preceding error, from own or others’ misperception or misinterpretation of information	Junior uses observation chart as a surrogate for current physiology and then provides insufficient oxygen to patient	Junior (D): “We had the patient on a Hudson [variable performance] mask… 97% sats [oxygen saturation] so I didn’t think we needed to jump in with all guns blazing.”
	Submission errors	Errors occurring when a junior doctor was dissuaded from taking the most appropriate course of action by a colleague advocating less appropriate measures	Aware patient is bleeding; one junior keen to use blood as primary resuscitation fluid but persuaded by other junior not to request any blood from blood bank	Junior (S): “I think we should just give more fluid.” Reply from other junior: “But if she’s bleeding blood then we should give her blood.” Junior: “…can we not just keep giving her saline, or jelly [colloid] or something?”