Related Experiment Video
Updated: Jul 4, 2026

Preliminary Study on Acupuncture Combined with Grain-sized Moxibustion for Treating Rheumatoid Arthritis with Finger Joint Pain
Published on: May 16, 2025
Repeated measures in rheumatoid arthritis reduced the required sample size in a two-armed clinical trial
Petter Mowinckel1, Kåre B Hagen, Turid Heiberg
1National Resource Centre for Rehabilitation in Rheumatology, Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.
Objectives:
To investigate whether repeated measures in patients with rheumatoid arthritis will reduce the between subject variation and if so, to determine the optimal number of measures to effectively reduce the number of participants required in controlled clinical trials.
Study Design And Setting:
A prospective observational study. Thirty-eight rheumatoid arthritis patients with a stable disease reported level of joint pain, fatigue and patient global assessment of disease activity on VAS scales as well as the Rheumatoid Arthritis Disease Activity Index (RADAI) daily during a total of 42 days.
Results:
In all measures, the variation within each individual was substantial over a 42-day period. By increasing the number of measurements from one to five, the standard deviation (SD) decreased from 5.5% (RADAI score) to 11% (Pain VAS) resulting in a reduction in the number of patients needed in a clinical trial from 11% to 22%, respectively. When we used from 6 to 42 individual measurements, the decrease continued but the reduction was of a smaller magnitude.
Conclusion:
The use of up to five repeated measurements per patient will decrease the number of patients required in a two armed clinical trial by as much as 22%.
Related Concept Videos
Bioequivalence Experimental Study Designs: Repeated Measures, Cross-Over, Carry-Over, and Latin Square Designs
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
Genome-wide Association Studies-GWAS
GWAS does not require the identification of the target gene involved in...
Crossover Experiments
Crossover designs are performed even with smaller sample sizes since the samples can act as their controls. These are better than simple randomized trials since patients are exposed to all the treatments.
Bioavailability Study Design: Single Versus Multiple Dose Studies
Bioavailability Study Design: Healthy Subjects Versus Patients