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Research Guides@Tufts

NUTR 230C: Interpreting Nutrition Evidence

Randomized Controlled Trial (RCT)


“A study design that randomly assigns participants into an experimental group or a control group. As the study is conducted, the only expected difference between the control and experimental groups in a randomized controlled trial (RCT) is the outcome variable being studied.”1

Why this type of study is used:

  • To reduces bias2
  • To approximate a controlled experiment.2
  • Statistically efficient2

Format and features:


Smoking reduction with oral nicotine inhalers: double blind, randomised clinical trial of efficacy and safety.

BMJ. 2000 Aug 5;321(7257):329-33.

Bolliger CT, Zellweger JP, Danielsson T, van Biljon X, Robidou A, Westin A, Perruchoud AP, Säwe U.


OBJECTIVES: To determine whether use of an oral nicotine inhaler can result in long term reduction in smoking and whether concomitant use of nicotine replacement and smoking is safe.

DESIGN: Double blind, randomised, placebo controlled trial. Four month trial with a two year follow up.

SETTING: Two university hospital pulmonary clinics in Switzerland.

PARTICIPANTS: 400 healthy volunteers, recruited through newspaper advertisements, willing to reduce their smoking but unable or unwilling to stop smoking immediately.

INTERVENTION: Active or placebo inhaler as needed for up to 18 months, with participants encouraged to limit their smoking as much as possible.

MAIN OUTCOME MEASURES: Number of cigarettes smoked per day from week six to end point. Decrease verified by a measurement of exhaled carbon monoxide at each time point compared with measurement at baseline.

RESULTS: At four months sustained reduction of smoking was achieved in 52 (26%) participants in the active group and 18 (9%) in the placebo group (P<0.001; Fisher's test). Corresponding figures after two years were 19 (9.5%) and 6 (3.0%) (P=0.012).

CONCLUSION: Nicotine inhalers effectively and safely achieved sustained reduction in smoking over 24 months. Reduction with or without nicotine substitution may be a feasible first step towards smoking cessation in people not able or not willing to stop abruptly.


  1. Himmelfarb Health Sciences Library (The George Washington University). Study Design 101: Randomized Controlled Trial. 2011; Accessed January 30, 2012.
  2. Grimes DA, Schulz KF. An overview of clinical research: the lay of the land. The Lancet. 1/5/ 2002;359(9300):57-61.
  3. The CONSORT Group. CONSORT 2010 checklist of information to include when reporting a randomised trial. 2010; Accessed January 31, 2013.