Then the proportional recovery rule needs to be tossed because the existing rehabilitation practices are a failure. The goal is 100% recovery NOT this justification for doctor and therapist failures.
What the Proportional Recovery Rule Is (and Is Not): Methodological and Statistical Considerations
Abstract
In
2008, it was proposed that the magnitude of recovery from nonsevere
upper limb motor impairment over the first 3 to 6 months after stroke,
measured with the Fugl-Meyer Assessment (FMA), is approximately 0.7
times the initial impairment (“proportional recovery”). In contrast to
patients with nonsevere hemiparesis, about 30% of patients with an
initial severe paresis do not show such recovery (“nonrecoverers”).
Hence it was suggested that the proportional recovery rule (PRR) was a
manifestation of a spontaneous mechanism that is present in all patients
with mild-to-moderate paresis but only in some with severe paresis.
Since the introduction of the PRR, it has subsequently been applied to
other motor and nonmotor impairments. This more general investigation of
the PRR has led to inconsistencies in its formulation and application,
making it difficult to draw conclusions across studies and precipitating
some cogent criticism. Here, we conduct a detailed comparison of the
different studies reporting proportional recovery and, where
appropriate, critique statistical methodology. On balance, we conclude
that existing data in aggregate are largely consistent with the PRR as a
population-level model for upper limb motor recovery; recent reports of
its demise are exaggerated, as these excessively focus on the less
conclusive issue of individual subject-level predictions. Moving
forward, we suggest that methodological caution and new analytical
approaches will be needed to confirm (or refute) a systematic character
to spontaneous recovery from motor and other poststroke impairments,
which can be captured by a mathematical rule either at the population or
at the subject level.
Introduction
Since it was introduced, the PRR has been applied in a broad range of studies that involve recovery from stroke, both for FMA-UE and for other outcomes. Claims related to the PRR have been made for upper and lower limb impairment measured by the FMA,3-10 aphasia measured with the Western Aphasia Battery (WAB),11 the resting motor threshold (RMT) of the extensor carpi radialis,6 and visuospatial neglect measured with the Letter Cancellation Test (LCT),12 among others. Applications of the PRR typically distinguish between two distinct subgroups of patients, referred to as “recoverers” and “nonrecoverers”: the former subgroup is composed of patients who recover a significant amount of lost function, and the latter is composed of those who do not. The PRR is thought to usefully characterize the recovery process among recoverers only. Although the methods by which the PRR was applied and evaluated have differed substantially across publications, many authors have argued that their findings are evidence for a PRR that accurately describes an underlying biological process that arises across neurolocical domains. Recently, however, the PRR has been the subject of criticism related to the validity of the statistical methods underlying its implementation and to the degree to which data are consistent with claims in support of the PRR.13,14 Much of the critique on the PRR articulated by these articles was focused on specific statements associated with the PRR followed by a general dismissal of all findings.
Our goal in this work is to provide a critical reexamination of the literature pertaining to the PRR. We focus first on the interpretation and implementation of PRR as a statistical model, and on data-driven concerns about the use of the PRR in studies of recovery. We then reexamine data reported in the literature and the extent to which past studies provide evidence for the PRR with these considerations in mind. Our hope is that this will serve as an instructive overview of issues that can arise in the application of the PRR to studies of recovery, aiming to improve future investigations into the PRR. Although our primary purpose is not to provide direct response to recent critiques,13,14 we are mindful of the concerns raised and address these directly in the Discussion section.
The breadth of work on the PRR introduces a commensurate range of methodological concerns one might consider. We attempt to be complete in our discussion but prefer to focus on overarching concerns regarding the statistical validity of the PRR instead of point-by-point inspections of the existing literature. Two themes we will revisit while pursuing the main goals of this paper are the identification of recoverers and the distinction between describing biological mechanisms and making patient-level predictions. The manner in which nonrecoverers are identified is a point of legitimate concern, as some statistical approaches can artifactually create evidence for the PRR. The PRR was originally intended to describe biological mechanisms at the population level, although implicitly it is expected that the PRR may be useful for predicting recovery of individual patients. Both of these are related to recent concerns regarding the PRR.
The next section provides an overview of the statistical formulation of the PRR and introduces three simulated datasets to illustrate scenarios over which the PRR shows varying degrees of validity. Subsequent sections conduct a selective review of the literature, reevaluating specific articles in the light of the three scenarios, comment on recent criticisms of the PRR, and end with our current view on the veracity of the PRR.
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