Analysing the Action Research Arm Test (ARAT): a cautionary tale from the RATULS trial.
Nina Wilson, Denise Howel, Helen Bosomworth and 2 others
PMID 33741815WHAT IT FOUND
The Action Research Arm Test subscales often produce U-shaped score distributions where patients score either zero or full marks.
Comparing average scores between groups is misleading. Clinicians should check data shape and use binary comparisons for these subscales.
Key findings
01In the RATULS trial, the distribution of the four Action Research Arm Test subscales at three months was U-shaped, with participants scoring either zero or full marks, making comparisons of means or medians inappropriate.
02The authors dichotomised the subscales to compare groups using logistic regression, defining success as completing at least one task in a subscale.
03Substantial floor effects were observed in both trials, with 80% of RATULS participants scoring the minimum on the pinch subscale at baseline and 71% at three months.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
This is a methodological analysis of existing trial data, not a new clinical trial, so it does not provide evidence on treatment efficacy. The findings rely on the specific patient populations in RATULS and BOTULS, who had moderate to severe upper limb limitation, so the distribution patterns may not apply to patients with mild impairment. The authors acknowledge that more sophisticated statistical techniques exist but chose a simple binary approach for interpretability, which may lose some information about the degree of ability.
Declared interests
The authors declared no conflicts of interest.
The easy way to misread this
Do not assume that mean scores from Action Research Arm Test subscale studies are valid comparisons. If the data is U-shaped or heavily skewed, as found in these trials, the mean is not a typical value and can lead to misleading conclusions about treatment effects.