Using the Barthel Index and modified Rankin Scale as outcome measures for stroke rehabilitation trials; a comparison of minimum sample size requirements

Kris McGill*, Catherine Sackley, Jon Godwin, David Gavaghan, Myzoon Ali, Belen Rubio Ballester, Marian C. Brady, VISTA-Rehabilitation collaborators

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)
145 Downloads (Pure)


Objectives: Underpowered trials risk inaccurate results. Recruitment to stroke rehabilitation randomised controlled trials (RCTs) is often a challenge. Statistical simulations offer an important opportunity to explore the adequacy of sample sizes in the context of specific outcome measures. We aimed to examine and compare the adequacy of stroke rehabilitation RCT sample sizes using the Barthel Index (BI) or modified Rankin Scale (mRS) as primary outcomes. Methods: We conducted computer simulations using typical experimental event rates (EER) and control event rates (CER) based on individual participant data (IPD) from stroke rehabilitation RCTs. Event rates are the proportion of participants who experienced clinically relevant improvements in the RCT experimental and control groups. We examined minimum sample size requirements and estimated the number of participants required to achieve a number needed to treat within clinically acceptable boundaries for the BI and mRS. Results: We secured 2350 IPD (18 RCTs). For a 90% chance of statistical accuracy on the BI a rehabilitation RCT would require 273 participants per randomised group. Accurate interpretation of effect sizes would require 1000s of participants per group. Simulations for the mRS were not possible as a clinically relevant improvement was not detected when using this outcome measure. Conclusions: Stroke rehabilitation RCTs with large sample sizes are required for accurate interpretation of effect sizes based on the BI. The mRS lacked sensitivity to detect change and thus may be unsuitable as a primary outcome in stroke rehabilitation trials.
Original languageEnglish
Article number106229
Number of pages7
JournalJournal of Stroke and Cerebrovascular Diseases
Issue number2
Early online date3 Dec 2021
Publication statusPublished - 1 Feb 2022


  • stroke rehabilitation
  • Barthel Index
  • modified Rankin Scale
  • sample size calculations
  • recruitment
  • simulations
  • randomised controlled trials

ASJC Scopus subject areas

  • Clinical Neurology
  • Cardiology and Cardiovascular Medicine
  • Rehabilitation
  • Surgery


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