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Related Concept Videos

Strategies for Assessing and Addressing Confounding01:25

Strategies for Assessing and Addressing Confounding

Confounding is a critical issue in epidemiological studies, often leading to misleading conclusions about associations between exposures and outcomes. It occurs when the relationship between the exposure and the outcome is mixed with the effects of other factors that influence the outcome. Given that, addressing confounding is of high importance for drawing accurate inferences in research.
Confounding can be addressed at both the design phase of a study and through analytical methods after data...
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.
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...
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...
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches01:23

Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches

Biopharmaceutical studies constitute a vital field aiming to enhance drug delivery methods and refine therapeutic approaches, drawing upon diverse interdisciplinary knowledge. In research methodologies, the choice between controlled and non-controlled studies significantly influences the study's reliability and accuracy.
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
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Bias

Bias refers to any tendency that prevents a question from being considered unprejudiced. In research, bias occurs when one outcome or answer is selected or encouraged over others in sampling or testing. Bias can occur during any research phase, including study design, data collection, analysis, and publication.
In statistics, a sampling bias is created when a sample is collected from a population, and some members of the population are not as likely to be chosen as others (remember, each member...

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Related Experiment Video

Updated: May 11, 2026

Online Repetitive Transcranial Magnetic Stimulation of Dorsomedial and Dorsolateral Prefrontal Cortex in Cognition Decision Making, and Cognitive Dissonance
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Do variations in allocation concealment methods influence the effects found in intervention reviews?

Cho Naing1, Syed Shahzad Hasan, Kyan Aung

  • 1International Medical University, Kuala Lumpur 57000, Malaysia. cho_naing@imu.edu.my

Journal of Evidence-Based Medicine
|May 16, 2013
PubMed
Summary

Liberal criteria in clinical trials can significantly alter intervention effect measures. This study highlights the critical importance of allocation concealment for reliable research findings.

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Area of Science:

  • Clinical Trial Methodology
  • Evidence-Based Medicine
  • Systematic Review Analysis

Background:

  • Cochrane reviews synthesize research findings.
  • Trial design criteria can influence reported intervention effects.
  • Ensuring the quality of evidence in systematic reviews is crucial.

Purpose of the Study:

  • To identify discrepancies in intervention effects between Cochrane reviews using liberal versus restrictive trial criteria.
  • To assess the impact of removing trials with liberal designs on effect measures.
  • To propose improvements for the quality of evidence in systematic reviews.

Main Methods:

  • Documentary analysis of three selected Cochrane reviews.
  • Two-stage sampling for Cochrane review selection.
  • Investigated the stability of effect measures after excluding trials with liberal designs.

Main Results:

  • Two of three reviews showed altered intervention effect measures after removing studies lacking allocation concealment.
  • One review reported an 87% greater relative risk with liberal design trials included.
  • Another review showed a 19.5% lower risk when liberal design trials were included.

Conclusions:

  • Instability of effect measures underscores the importance of allocation concealment in clinical trials.
  • Recommends further research with more intervention reviews and additional quality factors.
  • Emphasizes the need for rigorous methodological standards in systematic reviews.