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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...
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...
Sample Size Calculation01:19

Sample Size Calculation

Knowledge of the sample size is the first requirement to conduct random sampling or an experiment. The sample size is the total number of units, observations, or groups (in some cases) used to get the data to estimate a population parameter. As the name suggests, the sample size is that of the sample drawn from the population and differs from the population size.
The sample size for the given experiment or sampling effort is fundamental to any study design. Sample size decides the number of...
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...
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...
Testing a Claim about Population Proportion01:24

Testing a Claim about Population Proportion

A complete procedure for testing a claim about a population proportion is provided here.
There are two methods of testing a claim about a population proportion: (1) Using the sample proportion from the data where a binomial distribution is approximated to the normal distribution and (2) Using the binomial probabilities calculated from the data.
The first method uses normal distribution as an approximation to the binomial distribution. The requirements are as follows: sample size is large...

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Related Experiment Video

Updated: May 13, 2026

Measuring Maxillary Posterior Tooth Movement: A Model Assessment using Palatal and Dental Superimposition
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Measuring Maxillary Posterior Tooth Movement: A Model Assessment using Palatal and Dental Superimposition

Published on: February 23, 2024

Sample size in orthodontic randomized controlled trials: are numbers justified?

Despina Koletsi1, Nikolaos Pandis, Padhraig S Fleming

  • 1* Department of Orthodontics, School of Dentistry, University of Athens, Greece.

European Journal of Orthodontics
|March 6, 2013
PubMed
Summary

Sample size calculations are often reported in orthodontic randomized controlled trials (RCTs), but their presentation needs improvement. While calculations generally align with recruited numbers, less than 30% of studies fully report them.

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Area of Science:

  • Orthodontics
  • Clinical Trials Methodology

Background:

  • Sample size calculations are crucial for the statistical validity of randomized controlled trials (RCTs).
  • The Consolidated Standards of Reporting Trials (CONSORT) group recommends their reporting to ensure adequate power.
  • Orthodontic speciality journals are key venues for publishing RCTs in this field.

Purpose of the Study:

  • To analyze the reporting and performance of sample size calculations in orthodontic RCTs.
  • To assess the agreement between calculated and recruited sample sizes.
  • To identify factors influencing sample size reporting in orthodontic research.

Main Methods:

  • A systematic review of 139 RCTs published in orthodontic speciality journals.
  • Assessment of the completeness and accuracy of reported sample size calculations.
  • Analysis of study design, data analysis methods, and participant recruitment and attrition.

Main Results:

  • Only 29.5% of identified RCTs reported complete sample size calculations.
  • Parallel designs were most common (81%), typically with two arms.
  • Intention-to-treat analysis was used in only 13% of studies.
  • Median required sample size was 46, with a median recruitment of 60 participants and 4 lost to follow-up.
  • Good agreement was found between calculated and recruited numbers (median discrepancy: 5.3%).

Conclusions:

  • While sample size calculations are present in many orthodontic RCTs, their reporting quality is suboptimal.
  • Improvements in the transparency and completeness of sample size reporting are necessary.
  • Ensuring robust sample size justification is vital for the reliability of orthodontic research findings.