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Clinical Trials01:16

Clinical Trials

Clinical trials are prospective experimental studies conducted on humans to determine the safety and efficacy of treatments, drugs, diet methods, and medical devices. Using statistics in clinical trials enables researchers to derive reasonable and accurate conclusions from the collected data, allowing them to make wise decisions in uncertain situations. In medical research, statistical methods are crucial for preventing errors and bias.
There are four phases in a clinical trial. A phase one...
Clinical Trials: Overview01:11

Clinical Trials: Overview

Clinical development focuses on how the drug will interact with the human body and encompasses four key phases of clinical trials, each serving a specific purpose in assessing the safety and effectiveness of new drugs. These phases overlap and build upon one another. Phase I involves a small group of healthy volunteers (typically 20-80 individuals) or, in cases where significant toxicity is expected, patients with the targeted disease, such as cancer or AIDS. The volunteers are tested for...
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...
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: 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...

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Related Experiment Video

Updated: May 13, 2026

A Clinical Trial Assessing the Safety, Efficacy, and Delivery of Olive-Oil-Based Three-Chamber Bags for Parenteral Nutrition
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Intermediate outcomes in randomized clinical trials: an introduction.

Armando H Seuc1, Alexander Peregoudov, Ana Pilar Betran

  • 1Reproductive Health Research Department, World Health Organization, Geneva 27 1211, Switzerland. seuca@who.int

Trials
|March 21, 2013
PubMed
Summary

The intention-to-treat approach has limitations in randomized trials with intermediate outcomes. Principal stratification offers a more appropriate method for analyzing such complex causal pathways, as demonstrated in a calcium supplementation study.

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Area of Science:

  • Clinical Trials Methodology
  • Biostatistics
  • Causal Inference

Background:

  • Intermediate outcomes, such as noncompliance or pregnancy, are common in clinical trials and lie on the causal pathway to final outcomes.
  • Traditional intention-to-treat analysis may not adequately address these intermediate outcomes.
  • Alternative methods like principal stratification are less widely known but offer more appropriate analytical frameworks.

Purpose of the Study:

  • To highlight the limitations of the intention-to-treat approach for intermediate outcomes in experimental research.
  • To introduce and explain the principal stratification approach for handling intermediate outcomes.
  • To illustrate the application of principal stratification using a real-world clinical trial example.

Main Methods:

  • Introduced principal stratification and related concepts for causal effect estimation.
  • Discussed two methods for estimating causal effects.
  • Applied these methods to a long-term calcium supplementation trial, considering noncompliance and pregnancy as intermediate outcomes and preeclampsia as the final outcome.

Main Results:

  • Demonstrated the limitations of traditional methods when dealing with intermediate outcomes.
  • Detailed the steps, assumptions, and calculations required for applying principal stratification.
  • Illustrated the application within the context of the calcium trial.

Conclusions:

  • The intention-to-treat approach, while sound, is not universally applicable, especially for intermediate outcomes in randomized clinical trials.
  • Principal stratification provides a more suitable alternative for analyzing trials with intermediate outcomes.
  • Researchers should consider principal stratification when intermediate outcomes are present in their trial designs.