Kathryn S. Hayward,
In this entry, I discuss a recent publication by Rachel Hawe and colleagues (1) regarding the potential biases of the mathematical properties of the proportional recovery rule and how this may impact application in the field of stroke recovery. Proportional recovery is the idea that most individuals post-stroke (“fitters” to the rule) will recover 70% of their potential on a given outcome (see paper for rule equation). The authors cite multiple studies that have demonstrated proportional recovery for upper limb motor impairment using a single outcome (Fugl Meyer Upper Limb assessment, out of 66 points), and recent work extending this rule to lower limb, aphasia and hemispatial neglect recovery outcomes.
The principal mathematical concept discussed as a limitation of the proportional recovery rule is mathematical coupling. This concept refers to when one variable directly or indirectly contains all or a part of another. For example, in the case of proportional recovery of the upper limb post-stroke, the initial score on Fugl Meyer Upper Limb assessment is part of both the independent and dependent variables of the proportional recovery rule.