Determining Levels of Evidence

Interpreting the Results of Individual Studies

For RCTs, studies scoring 9-10 on the PEDro scale were considered to be of “excellent” methodologically quality, 6-8 of “good” quality, 4-5 of “fair” quality, and below 4 of “poor” quality. The authors determined these descriptive terms of quality assessment in an effort to simplify the interpretation of results. Studies employing a non-experimental or uncontrolled design were used to formulate conclusions only in the absence of RCTs.

Formulating Conclusions Based on Levels of Evidence

The levels of evidence (table found below) used to summarize the findings are based on the levels of evidence developed by Sackett et al. (2000). The levels proposed by Sackett et al. (2000) have been modified; specifically the original ten categories have been reduced to five levels. Level 1 evidence pertains to high quality RCTs (PEDro ≥6) and has been divided into two subcategories, level 1a and level 1b, based on the number of RCTs supporting the evidence statement.

Using this system, conclusions were easily formed when the results of multiple studies were in agreement. However, in cases where RCTs differed in conclusions and methodological quality, the results of the study (or studies) with the higher PEDro score(s) were more heavily weighted. In rare instances the authors needed to make a judgment when the results of a single study of higher quality conflicted with those of several studies of inferior quality. In these cases we attempted to provide a rationale for our decision and to make the process as transparent as possible. In the end the reader is encouraged to be a “critical consumer” of all of the material presented.

Table: Levels of Evidence

Level

Research Design

Description

Level 1a

Randomized Controlled Trial (RCT)

More than 1 RCT with PEDro score ≥ 6.

Includes within subjects comparison with randomized conditions and crossover designs.

Level 1b

RCT

1 RCT with PEDro ≥ 6.

Level 2

RCT

RCT, PEDro < 6.

Prospective controlled trial

Prospective controlled trial (not randomized).

Cohort

Prospective longitudinal study using at least two similar groups with one exposed to a particular condition.

Level 3

Case Control

A retrospective study comparing conditions including historical controls.

Level 4

Pre-Post test

A prospective trial with a baseline measure, intervention, and a post- test using a single group of subjects.

Post-test

A prospective intervention study using a post intervention measure only (no pre-test or baseline measurement) with one or more groups

Case Series

A retrospective study usually collecting variables from a chart review.

Level 5

Observational Study

Using cross sectional analysis to interpret relations

Clinical Consensus

Expert opinion without explicit critical appraisal, or based on physiology, biomechanics or “first principles”.

Case Reports

Pre-post or case series involving one subject.