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Related Concept Videos

Randomized Experiments01:13

Randomized Experiments

The randomization process involves assigning study participants randomly to experimental or control groups based on their probability of being equally assigned. Randomization is meant to eliminate selection bias and balance known and unknown confounding factors so that the control group is similar to the treatment group as much as possible. A computer program and a random number generator can be used to assign participants to groups in a way that minimizes bias.
Simple randomization
Simple...
Blinding01:11

Blinding

Blinding is a commonly used method of not telling participants which treatment a subject is receiving. Blinding is a critical part of a randomized control trial or RCT. It reduces the bias that affects the results. In an RCT, blinding is used in the form of a placebo. A placebo effect occurs when untreated subjects falsely believe they have received the treatment and report improved symptoms. A placebo or a dummy treatment is administered to subjects to negate the bias caused by such an effect.
Bioequivalence Experimental Study Designs: Repeated Measures, Cross-Over, Carry-Over, and Latin Square Designs01:15

Bioequivalence Experimental Study Designs: Repeated Measures, Cross-Over, Carry-Over, and Latin Square Designs

Bioequivalence experimental study designs play a pivotal role in testing the effectiveness of various treatments. Key among these are the repeated measures, cross-over, carry-over, and Latin square designs. In the repeated measures design, each subject receives all treatments, allowing for temporal comparisons. This type of design is useful in reducing variability but requires careful planning to avoid bias.The cross-over design, an economical method, involves sequential administration of...
Group Design02:01

Group Design

The most basic experimental design involves two groups: the experimental group and the control group. The two groups are designed to be the same except for one difference— experimental manipulation. The experimental group gets the experimental manipulation—that is, the treatment or variable being tested—and the control group does not. Since experimental manipulation is the only difference between the experimental and control groups, we can be sure that any differences between the two are due to...
Bioequivalence Experimental Study Designs: Completely Randomized and Randomized Block Designs01:20

Bioequivalence Experimental Study Designs: Completely Randomized and Randomized Block Designs

Bioequivalence experimental study designs are crucial methodologies used in evaluating and comparing the bioavailability of different drug products. These designs are categorized into various types: completely randomized, randomized block, repeated measures, cross and carry-over, and Latin square designs.Completely randomized designs involve randomly allocating treatments to all subjects participating in the experiment. This allocation is achieved by assigning unique random numbers to subjects...
Blind Procedures02:07

Blind Procedures

Ideally, the people who observe and record the children’s behavior are unaware of who was assigned to the experimental or control group, in order to control for experimenter bias. Experimenter bias refers to the possibility that a researcher’s expectations might skew the results of the study. Remember, conducting an experiment requires a lot of planning, and the people involved in the research project have a vested interest in supporting their hypotheses. If the observers knew which child was...

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Updated: Jun 29, 2026

A Within-Subject Experimental Design using an Object Location Task in Rats
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A Within-Subject Experimental Design using an Object Location Task in Rats

Published on: May 6, 2021

[Pre-randomisation in study designs: getting past the taboo].

R Schellings1, A G Kessels, F Sturmans

  • 1Gezondheidszorg, Postbus 900.37, 5200 MA Den Bosch. ag.schellings@igz.nl

Nederlands Tijdschrift Voor Geneeskunde
|October 8, 2008
PubMed
Summary
This summary is machine-generated.

Pre-randomisation in clinical trials reverses the usual order of consent and randomisation. This design is permissible under specific ethical and methodological conditions for valid intervention evaluation.

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Area of Science:

  • Clinical Trials Methodology
  • Research Ethics

Background:

  • Pre-randomisation reverses the standard sequence of informed consent and randomisation in study designs.
  • The Dutch Ministry of Health, Welfare and Sport permits pre-randomisation under specific conditions.
  • The Zelen design randomises participants before obtaining consent, with consent sought only for the experimental group.

Discussion:

  • Ethical, legal, and methodological objections to pre-randomisation are increasingly recognised.
  • Pre-randomisation has historically been underutilised or misused.
  • Awareness of its complexities is growing within the research community.

Key Insights:

  • Pre-randomisation is justified when conventional randomised designs impede valid intervention effect evaluation (e.g., due to non-compliance or drop-out).
  • It is particularly applicable for interventions like educational programmes where knowledge of the intervention influences behaviour.
  • The procedure requires a clinically relevant objective, potential for significant new insights, and no harm during consent.

Outlook:

  • Strict ethical and methodological criteria must be met for pre-randomisation.
  • Informed consent procedures must pose no harm to participants.
  • Approval from an independent research ethics committee is mandatory, ensuring participant safety and study integrity.