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Research Guides@Tufts

Study Designs in the Health Sciences

An introduction to the main features and uses of study designs popular and unique to medicine and the health sciences.

Randomized Controlled Trial (RCT)

What is a 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 use this type of study?

  • To reduces bias [2]
  • To approximate a controlled experiment.[2]
  • Statistically efficient [2]

Format and features


  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.


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.