Construct validity of the Physiotherapy Evidence Database (PEDro) quality scale for randomized trials: Item response theory and factor analyses.

Emiliano Albanese,Matthias Egger,Lukas Bütikofer,Susan Armijo‐Olivo,Christine Ha

doi:10.1002/jrsm.1385

Abstract

BackgroundThere is an agreement that the methodological quality of randomized trials should be assessed in systematic reviews, but there is a debate on how this should be done. We conducted a construct validation study of the Physiotherapy Evidence Database (PEDro) scale, which is widely used to assess the quality of trials in physical therapy and rehabilitation.MethodsWe analyzed 345 trials that were included in Cochrane reviews and for which a PEDro summary score was available. We used one‐ and two‐parameter logistic item response theory (IRT) models to study the psychometric properties of the PEDro scale and assessed the items' difficulty and discrimination parameters. We ran goodness of fit post estimations and examined the IRT unidimensionality assumption with a multidimensional IRT (MIRT) model.ResultsOut of a maximum of 10, the mean PEDro summary score was 5.46 (SD = 1.51). The allocation concealment and intention‐to‐treat scale items contributed most of the information on the underlying construct (with discriminations of 1.79 and 2.05, respectively) at similar difficulties (0.63 and 0.65, respectively). The other items provided little additional information and did not distinguish trials of different quality. There was substantial evidence of departure from the unidimensionality assumption, suggesting that the PEDro items relate to more than one latent trait.ConclusionsOur findings question the construct validity of the PEDro scale to assess the methodological quality of clinical trials. PEDro summary scores should not be used; rather, the physiotherapy community should consider working with the individual items of the scale.

Highlights

Systematic reviews and meta-analyses of randomized trials have a pivotal role informing clinical practice and policy decisions,[1] and there is a broad agreement that the methodological quality of primary studies should be carefully assessed
We focus on the Physiotherapy Evidence Database (PEDro) scale, which is widely used to assess the methodological quality of clinical trials in the field of physical therapy and rehabilitation
We found that the scale items used to compute the PEDro study quality score captured more than one underlying trait

Summary

Background

There is an agreement that the methodological quality of randomized trials should be assessed in systematic reviews, but there is a debate on how this should be done. We conducted a construct validation study of the Physiotherapy Evidence Database (PEDro) scale, which is widely used to assess the quality of trials in physical therapy and rehabilitation. We used one- and two-parameter logistic item response theory (IRT) models to study the psychometric properties of the PEDro scale and assessed the items' difficulty and discrimination parameters. There was substantial evidence of departure from the unidimensionality assumption, suggesting that the PEDro items relate to more than one latent trait. Conclusions: Our findings question the construct validity of the PEDro scale to assess the methodological quality of clinical trials. PEDro summary scores should not be used; rather, the physiotherapy community should consider working with the individual items of the scale. KEYWORDS item response theory, physiotherapy, randomized clinical trials, risk of bias, study quality scale, validation

| INTRODUCTION

| METHODS

| Statistical methods

| RESULTS

Findings

| DISCUSSION