PEDro scale

The PEDro scale was last amended on 21 June 1999.

This briefly explains why each item has been included in the PEDro scale. More detail on each item is provided in the PEDro scale training program.

1. eligibility criteria were specified

Note on administration: 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.

Explanation: This criterion influences external validity, but not the internal or statistical validity of the trial. It has been included in the PEDro scale so that all items of the Delphi scale are represented on the PEDro scale. This item is not used to calculate the PEDro score.

2. subjects were randomly allocated to groups (in a crossover study, subjects were randomly allocated an order in which treatments were received)

Note on administration: A study is considered to have used random allocation if the report states that allocation was random. The precise method of randomisation need not be specified. Procedures such as coin-tossing and dice-rolling should be considered random. Quasi-randomised allocation procedures such as allocation by hospital record number or birth date, or alternation, do not satisfy this criterion.

Explanation: Random allocation ensures that (within the constraints provided by chance) treatment and control groups are comparable.

3. allocation was concealed

Note on administration: 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. 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”.

Explanation: “Concealment” refers to whether the person who determined if subjects were eligible for inclusion in the trial was aware, at the time he or she made this decision, which group the next subject would be allocated to. Potentially, if allocation is not concealed, the decision about whether or not to include a person in a trial could be influenced by knowledge of whether the subject was to receive treatment or not. This could produce systematic biases in otherwise random allocation. There is empirical evidence that concealment predicts effect size (concealment is associated with a finding of more modest treatment effects; see Schulz et al (1995) JAMA 273:408-412).

4. the groups were similar at baseline regarding the most important prognostic indicators

Note on administration: 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. 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. This criterion is satisfied even if only baseline data of study completers are presented.

Explanation: This criterion may provide an indication of potential bias arising by chance with random allocation. Gross discrepancies between groups may be indicative of inadequate randomisation procedures.

5. there was blinding of all subjects

Note on administration: Blinding means the person in question (subject, therapist or assessor) did not know which group the subject had been allocated to. In addition, subjects and therapists are only considered to be “blind” if it could be expected that they would have been unable to distinguish between the treatments applied to different groups. In trials in which key outcomes are self-reported (eg, visual analogue scale, pain diary), the assessor is considered to be blind if the subject was blind.

Explanation: Blinding of subjects involves ensuring that subjects were unable to discriminate whether they had or had not received the treatment. When subjects have been blinded, the reader can be satisfied that the apparent effect (or lack of effect) of treatment was not due to placebo effects or Hawthorne effects (an experimental artifact in which subjects responses are distorted by how they expect the experimenters want them to respond).

6. there was blinding of all therapists who administered the therapy

Note on administration: Blinding means the person in question (subject, therapist or assessor) did not know which group the subject had been allocated to. In addition, subjects and therapists are only considered to be “blind” if it could be expected that they would have been unable to distinguish between the treatments applied to different groups. In trials in which key outcomes are self-reported (eg, visual analogue scale, pain diary), the assessor is considered to be blind if the subject was blind.

Explanation: Blinding of therapists involves ensuring that therapists were unable to discriminate whether individual subjects had or had not received the treatment. When therapists have been blinded, the reader can be satisfied that the apparent effect (or lack of effect) of treatment was not due to the therapists’ enthusiasm or lack of enthusiasm for the treatment or control conditions.

7. there was blinding of all assessors who measured at least one key outcome

Note on administration: Blinding means the person in question (subject, therapist or assessor) did not know which group the subject had been allocated to. In addition, subjects and therapists are only considered to be “blind” if it could be expected that they would have been unable to distinguish between the treatments applied to different groups. In trials in which key outcomes are self-reported (eg, visual analogue scale, pain diary), the assessor is considered to be blind if the subject was blind.

Explanation: Blinding of assessors involves ensuring that assessors were unable to discriminate whether individual subjects had or had not received the treatment. When assessors have been blinded, the reader can be satisfied that the apparent effect (or lack of effect) of treatment was not due to the assessors’ biases impinging on their measures of outcomes.

8. measures of at least one key outcome were obtained from more than 85% of the subjects initially allocated to groups

Note on administration: This criterion is only satisfied if the report explicitly states both the number of subjects initially allocated to groups and the number of subjects from whom key outcome measures were obtained. 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.

Explanation: It is important that measurement of outcome are made on all subjects who are randomised to groups. Subjects who are not followed up may differ systematically from those who are, and this potentially introduces bias. The magnitude of the potential bias increases with the proportion of subjects not followed up.

9. 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”

Note on administration: 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. 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.

Explanation: Almost inevitably there are protocol violations in clinical trials. Protocol violations may involve subjects not receiving treatment as planned, or receiving treatment when they should not have. Analysis of data according to how subjects were treated (instead of according to how subjects should have been treated) may produce biases. It is probably important that, when the data are analysed, analysis is done as if each subject received the treatment or control condition as planned. This is usually referred to as “analysis by intention to treat”. For a discussion of analysis by intention to treat see Hollis S & Campbell F (1999) BMJ 319:670-674.

10. the results of between-group statistical comparisons are reported for at least one key outcome

Note on administration: A between-group statistical comparison involves statistical comparison of one group with another. Depending on the design of the study, this may involve comparison of two or more treatments, or comparison of treatment with a control condition. 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 (when a factorial analysis of variance has been used to analyse the data, the latter is often reported as a group x time interaction). 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, or number needed to treat, or a relative risk or hazard ratio) and its confidence interval.

Explanation: In clinical trials, statistical tests are performed to determine if the difference between groups is greater than can plausibly be attributed to chance.

11. the study provides both point measures and measures of variability for at least one key outcome

Note on administration: 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. Measures of variability include standard deviations, standard errors, confidence intervals, interquartile ranges (or other quantile ranges), and ranges. Point measures and/or measures of variability may be provided graphically (for example, SDs may be given as error bars in a Figure) as long as it is clear what is being graphed (for example, as long as it is clear whether error bars represent SDs or SEs). Where outcomes are categorical, this criterion is considered to have been met if the number of subjects in each category is given for each group.

Explanation: Clinical trials potentially provide relatively unbiased estimates of the size of treatment effects. The best estimate (point estimate) of the treatment effect is the difference between (or ratio of) the outcomes of treatment and control groups. A measure of the degree of uncertainty associated with this estimate can only be calculated if the study provides measures of variability.

For all criteria

Points are only awarded when a criterion is clearly satisfied. If on a literal reading of the trial report it is possible that a criterion was not satisfied, a point should not be awarded for that criterion.

For criteria 4 and 7-11

Key outcomes are those outcomes which provide the primary measure of the effectiveness (or lack of effectiveness) of the therapy. In most studies, more than one variable is used as an outcome measure.

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