In systematic reviews statistical pooling is not always possible due to inadequate reporting of the results of original studies. In these reviews, a qualitative analysis using levels of evidence may be performed to summarize the evidence and to formulate conclusions [
]. This is explicit and reproducible, because it explains the exact meaning of labels like strong, moderate, and limited evidence. In the course of time, different sets of levels of evidence have been published [
- Van Tulder M.
- Koes B.W.
- Bouter L.M.
Conservative treatment of acute and chronic non specific low back pain. A systematic review of randomized controlled trials of the most common interventions.
Spine. 1997; 22: 2128-2156
- Van Tulder M.W.
- Ostelo R.
- Vlaeyen J.W.S.
- Linton S.J.
- Morley S.J.
- Assendelft W.J.J.
Behavioural treatment for chronic low back pain: a systematic review within the framework of the Cochrane Collaboration Back Review Group.
Spine. 2000; 25: 2688-2699
- Van Poppel M.N.M.
- Koes B.W.
- Smid T.
- Bouter L.M.
A systematic review of controlled clinical trials on the prevention of low back pain in industry.
Occup Environ Med. 1997; 54: 841-847
- Van der Windt D.A.W.N.
- Van der Heijden G.J.M.G.
- Van der Berg S.G.M.
- Ter Riet G.
- De Winter A.F.
- Bouter L.M.
Ultrasound therapy for musculoskeletal disorders: a systematic review.
Pain. 1999; 81: 257-271
5]. All these sets are arbitrary and based on common sense at best. Ferreira et al. [
- Berghmans L.C.M.
- Hendriks H.J.M.
- Bo K.
- Hay -Smith E.J.
- De Bie R.A.
- Van Doorn E.S.C.V.W.
Conservative treatment of stress urinary incontinence in women: a systematic review of randomised clinical trials.
Br J Urol. 1998; 82: 181-191
] show in their article that these different criteria may lead to different conclusions. They advise readers to be cautious when interpreting conclusions of systematic reviews that use levels of evidence. We fully agree, but not merely because different sets of criteria exist. If only one set of levels of evidence would exist this warning would even be more necessary. The use of levels of evidence is essentially an arbitrary and subjective way of summarizing evidence. Typically levels of evidence take into account the quality of the studies and the consistency of the results. In contrast to meta-analysis (statistical pooling), levels of evidence do not include the size of the effect. In the interpretation of both the conclusions of a study and its methodologic quality, there is some subjectivity involved. For example, grading the conclusions is difficult when there is borderline statistical significance, when a positive effect is observed for only part of many outcome measures studied, or when the reviewers do not agree with the authors' conclusions.
- Ferreira P.H.
- Ferreira M.L.
- Maher C.G.
- Refshauge K.
- Herbert R.D.
- Latimer J.
Effect of applying different “levels of evidence” criteria on conclusions of Cochrane reviews of interventions for low back pain.
J Clin Epidemiol. 2002; 55: 1126-1129
To read this article in full you will need to make a payment
Purchase one-time access:Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
One-time access price info
- For academic or personal research use, select 'Academic and Personal'
- For corporate R&D use, select 'Corporate R&D Professionals'
Subscribe:Subscribe to Journal of Clinical Epidemiology
Already a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
- Conservative treatment of acute and chronic non specific low back pain. A systematic review of randomized controlled trials of the most common interventions.Spine. 1997; 22: 2128-2156
- Behavioural treatment for chronic low back pain: a systematic review within the framework of the Cochrane Collaboration Back Review Group.Spine. 2000; 25: 2688-2699
- A systematic review of controlled clinical trials on the prevention of low back pain in industry.Occup Environ Med. 1997; 54: 841-847
- Ultrasound therapy for musculoskeletal disorders: a systematic review.Pain. 1999; 81: 257-271
- Conservative treatment of stress urinary incontinence in women: a systematic review of randomised clinical trials.Br J Urol. 1998; 82: 181-191
- Effect of applying different “levels of evidence” criteria on conclusions of Cochrane reviews of interventions for low back pain.J Clin Epidemiol. 2002; 55: 1126-1129
- The measurement of observer agreement for categorical data.Biometrics. 1997; 33: 159-174
- The design and analysis of clinical experiments.John Wiley & Sons, New York1986
- High agreement but low kappa: I. The problem of two paradoxes.J Clin Epidemiol. 1990; 43: 543-549
- The hazards of scoring the quality of clinical trials for meta-analysis.JAMA. 1999; 282: 1054-1060
- Corticosteroid injections for lateral epicondylitis: a systematic review.Pain. 2002; 96: 23-40
- Updated method guidelines for systematic reviews in the Cochrane Collaboration Back Review Group.Spine. 2003; 28: 1290-1299
Accepted: March 12, 2003
© 2003 Elsevier Inc. Published by Elsevier Inc. All rights reserved.