Pedro Scale

PEDRO Scale Danish Hassan Riphah International University

What is the PEDro scale 

Clinical trials indexed on the PEDro database are rated with a checklist called the "PEDro scale"

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Developed to help the users of the PEDro database to rapidly identify clinical trials that are likely to be internally valid and have sufficient statistical information to make their results interpretable

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The PEDro scale considers two aspects of trial quality, namely the 1. Believability / Internal Validity (Item 2-9) 2. Whether The Trial Contains Sufficient Statistical Information To Make It Interpretable (Items 10-11)

ITEM: 1 Eligibility Criteria And Source

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Criterion: This criterion is satisfied if the report describes the source of subjects and a list of criteria used to determine who was eligible to participate in the study.

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PEDro scale item 1 relates to external validity or generalisability, but not the internal validity or statistical reporting of the trial. Because it does not evaluate internal validity or statistical reporting it is not included in the PEDro score.

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To fulfill this item the report needs to describe BOTH the source of subjects AND the eligibility criteria used to select subjects. If only one aspect is described it would score a ‘no’

ITEM 2: Random Allocation 

Criterion: Subjects were randomly allocated to groups

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A study is considered to have used random allocation if the report states that allocation was random.

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The precise method of randomisation need not be specified. 

Procedures such as coin-tossing and dice-rolling should be considered random.

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Quasi-randomisation allocation procedures such as allocation by hospital record number or birth date, or alternation, do not satisfy this criterion.

ITEM 3: Concealed Allocation 

Criterion: Allocation was concealed

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Concealed allocation means that the person who determined if a subject was eligible for inclusion in the trial was unaware, when this decision was made, of which group the subject would be allocated to.

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A point is awarded for this criteria, even if it is not stated that allocation was concealed, when the report states that allocation was by sealed opaque envelopes or that allocation involved contacting the holder of the allocation schedule who was “off-site” or “not otherwise involved in the study”.

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Concealment of allocation is “the process used to ensure that the person deciding to enter a participant into a randomised controlled trial does not know the comparison group into which that individual will be allocated.

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This is distinct from blinding, and is aimed at preventing selection bias”

ITEM 4: Baseline comparability 

Criterion: The groups were similar at baseline regarding the most important prognostic indicators

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At a minimum, in studies of therapeutic interventions, the report must describe at least one measure of the severity of the condition being treated and at least one (different) key outcome measure at baseline.

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The rater must be satisfied that the groups’ outcomes would not be expected to differ, on the basis of baseline differences in prognostic variables alone, by a clinically significant amount.

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This criterion is satisfied even if only baseline data of study completers are presented.

ITEMS 5, 6 AND 7: Blinding of subjects, therapists and assessors 

These three items on the PEDro scale deal with blinding or masking, and will be considered together.

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Criterion 5: There was blinding of all subjects

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Criterion 6: There was blinding of all therapists who administered the therapy

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Criterion 7: There was blinding of all assessors who measured at least one key outcome

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Blinding means the person in question (subject, therapist or assessor) did not know which group the subject had been allocated to.

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Blinding of subjects involves ensuring that subjects were unable to discriminate whether they had or had not received the treatment

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Blinding of therapists involves ensuring that therapists were unable to discriminate whether individual subjects had or had not received the treatment

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Blinding of assessors involves ensuring that assessors were unable to discriminate whether individual subjects had or had not received the treatment

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Reports sometimes use the terms single-blind, double-blind and triple-blind. The problem with using these terms is that there are no accepted definitions, so that the same terms may be used to describe different types of blinding in different trials.

ITEM 8: Adequate follow-up 

Criterion: Measures of at least one key outcome were obtained from more than 85% of the subjects initially allocated to groups

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In trials in which outcomes are measured at several points in time, a key outcome must have been measured in more than 85% of subjects at one of those points in time.

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The rater needs to judge which outcomes are key outcomes and which follow-up periods are key follow-up periods.

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The cut-off is 85%, so if ≤ 85% of subjects initially allocated to groups have data for a key outcome at follow-up the record will score a ‘no’ for this item while if > 85% of subjects initially allocated to groups have data for a key outcome at follow-up will score a ‘yes’.

ITEM 9: Intention-to-treat analysis 

Criterion: All subjects for whom outcome measures were available received the treatment or control condition as allocated or, where this was not the case, data for at least one key outcome was analysed by “intention to treat”

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An intention-to-treat analysis means that, where subjects did not receive treatment (or the control condition) as allocated and where measures of outcomes were available, the analysis was performed as if subjects received the treatment (or control condition) they were allocated to.

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This criterion is satisfied, even if there is no mention of analysis by intention to treat, if the report explicitly states that all subjects received treatment or control conditions as allocated.

ITEM 10: Between-group comparisons 

A between-group statistical comparison involves statistical comparison of one group with another.

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Depending on the design of the study, this may involve comparison of two or more treatments, or comparison of treatment with a control condition.

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The analysis may be a simple comparison of outcomes measured after the treatment was administered, or a comparison of the change in one group with the change in another.

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The comparison may be in the form of hypothesis testing (which provides a “p” value, describing the probability that the groups differed only by chance) or in the form of an estimate (for example, the mean or median difference, or a difference in proportions, the number needed to treat, a relative risk or a hazard ratio) and its confidence interval.

ITEM 11: Point estimates and variability 

Criterion: The study provides both point measures and measures of variability for at least one key outcome

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A point measure is a measure of the size of the treatment effect. The treatment effect may be described as a difference in group outcomes, or as the outcome in (each of) all groups. 

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Measures of variability include standard deviations, standard errors, confidence intervals, interquartile ranges (or other quartile ranges), and ranges.

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For continuous data, the type of point estimate (eg, mean or median) and the type of variability (eg, standard deviation or standard error) needs to be specified.

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For categorical data (eg, ‘able to walk independently’ versus ‘not able to walk independently’), this criterion is achieved if the number of subjects in each category for each group are reported.