How are trials rated?
Trials (but not reviews or guidelines) are rated with a checklist (called the “PEDro scale”). The PEDro scale considers two aspects of trial quality, namely the “believability” of the trial and whether the trial contains sufficient statistical information to make it interpretable. “generalisability” of the trial or the size of the treatment effect. All but two of the PEDro scale items are based on the Delphi list, developed by Verhagen and colleagues. The Delphi list is a list of trial characteristics that was thought to be related to trial “quality” by a group of clinical trial experts (for details see Verhagen et al, Journal of Clinical Epidemiology 51: 1235-41, 1998). The PEDro scale contains additional items on adequacy of follow-up and between-group statistical comparisons. One item on the Delphi list (the item on eligibility criteria) is related to external validity, so it does not reflect the dimensions of quality assessed by the PEDro scale. This item is not used to calculate t
Trials (but not reviews or guidelines) are rated with a checklist (called the “PEDro scale”). The PEDro scale considers two aspects of trial quality, namely the “believability” (or “internal validity”) of the trial and whether the trial contains sufficient statistical information to make it interpretable. It does not rate the “meaningfulness” (or “generalisability” or “external validity”) of the trial, or the size of the treatment effect. To assess believability we look for unambiguous confirmation of a number of criteria, including random allocation, concealment of allocation, comparability of groups at baseline, blinding of patients, therapists and assessors, analysis by intention to treat and adequacy of follow-up. To assess interpretability we look for between-group statistical comparisons and reports of both point estimates and measures of variability. This gives a total of 10 scale items. Trials are rated on the basis of what they report. If a trial does not report that a particu
