Clinician-trialist rounds: 5. Cointervention bias – how to diagnose it in their trial and prevent it in yours

North American Symptomatic Carotid Endarterectomy Trial (NASCET) Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl J Med 1991; 325: 445–53.

The FIELD Study Investigators. Effects of long-term fenofibrate therapy on cardiovascular events in 9795 people with type 2 diabetes mellitus (the FIELD study): randomised controlled trial. Lancet 2005; 366: 1849–61.

The CLOTS (Clots in Legs Or sTockings after Stroke) Trial Collaboration. Thigh-length versus below-knee stockings for deep venous thrombosis prophylaxis after stroke: a randomized trial. Ann Intern Med 2010; 153: 553–62.

Haynes RB Sackett DL Guyatt GH Tugwell P . The principles behind the tactics of performing therapeutic trials. Clinical Epidemiology: How to Do Clinical Practice Research 2006; Chapter 6, 3rd. Lippincott Williams & Wilkins, Philadelphia, 183–8.