Table 5.

Examples of published randomised controlled trials (RCTs) in surgery requiring different amounts of standardisation of the interventions

Factors contributing to the level of control required	Example of RCTs requiring less standardisation	Example of RCTs requiring more standardisation
Scope of the trial	Comparison of surgery and medical therapy for treatment of gastro-oesophageal reflux disease [26]	Carotid artery stenting compared with endarterectomy in patients with carotid stenosis [27]
Pragmatic versus explanatory approach to design	Pragmatic: The trial aimed to establish the effectiveness of the interventions in practice	Explanatory: The trial aimed to establish the safety and efficacy of the ‘new’ intervention (stenting) under ideal conditions
Stage of innovation of the intervention	Open versus minimally invasive surgery for colorectal cancer [28]	Endovascular versus open repair of abdominal aortic aneurysms [29]
Established versus new innovation	Established: Open colorectal surgery is routinely undertaken by many operators in clinical practice and the main steps are already known	Early: Endovascular aneurysm repair is a relatively new technique and the main steps are less well known
Complexity of the intervention	Effect of an implantable gentamicin-collagen sponge on sternal wound infections following cardiac surgery [30]	Extracranial-intracranial bypass surgery for stroke prevention in hemodynamic cerebral ischemia [31]
Few components and low technical difficulty versus multiple components or requiring highly complex skills	Low complexity: Intervention involves placing an antibiotic impregnated sponge beneath patients’ wounds prior to closure	High complexity: Intervention is complex involving multiple components, high levels of technical expertise and multiple concomitant interventions
Nature of interventions being compared	Amoxicillin plus clavulanic acid versus appendicectomy for treatment of acute uncomplicated appendicitis [32]	Laparoscopic gastric bypass versus laparoscopic duodenal switch for super obesity [33]
Surgical and non-surgical intervention, or different surgical interventions	Surgery versus non-surgery: Distinction between trial groups is straightforward because of the very different nature of interventions	Surgery versus surgery: Distinction between the two groups is less straightforward because both interventions are surgical