Using the Zelen design in randomized controlled trials: debates and controversies

J Adv Nurs. 2002 Apr;38(2):200-7. doi: 10.1046/j.1365-2648.2002.02164.x.


Background: The use of the randomized consent design (commonly known as the Zelen design) is a controversial issue in randomized controlled trials. In the Zelen design, participants are randomly allocated prior to seeking consent. Those participants allocated to the intervention group are then approached and offered the intervention, which they can decline or accept. Zelen first proposed the design in 1979. It has been used infrequently since this time, although there are some notable exceptions in nursing, midwifery and some medical specialities.

Aim: This paper describes the Zelen design, including the two forms used (the single and double consent versions) and discusses the advantages and disadvantages of using such a design.

Methods: An explanation of the differences between the Zelen design and a conventional randomized controlled trial is presented. In a conventional design, detailed knowledge of the alternative interventions is given to the prospective participant. The participant gives consent and is allocated to one of the groups. In a Zelen design, participants are randomly allocated and then approached and offered the group to which they were allocated. The Zelen design is used firstly, to reduce disappointment bias in the conventional consent-randomization process, and secondly, to remove subjective bias in the recruitment process. There are concerns relating to the use of the Zelen design, including ethical concerns relating to the timing of random allocation and consent and the collection of clinical data.

Conclusion: It is hoped that by presenting issues pertaining to the Zelen design, other nursing and midwifery researchers may be prompted to consider its use when designing clinical research. The Zelen design is controversial, and debate about its merits and shortcomings is useful. This paper contributes to the ongoing debate.

Publication types

  • Review

MeSH terms

  • Ethics, Nursing
  • Humans
  • Informed Consent*
  • Midwifery / standards
  • Models, Nursing
  • New Zealand
  • Nurse Midwives / standards
  • Nursing Evaluation Research / organization & administration*
  • Patient Advocacy
  • Patient Selection*
  • Randomized Controlled Trials as Topic* / legislation & jurisprudence
  • Randomized Controlled Trials as Topic* / methods*
  • Randomized Controlled Trials as Topic* / standards
  • Research Design / legislation & jurisprudence
  • Research Design / standards*
  • Selection Bias
  • Time Factors
  • Truth Disclosure