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01.12.2015 | Research Article | Ausgabe 1/2015 Open Access

BMC Musculoskeletal Disorders 1/2015

The effect of journal impact factor, reporting conflicts, and reporting funding sources, on standardized effect sizes in back pain trials: a systematic review and meta-regression

BMC Musculoskeletal Disorders > Ausgabe 1/2015
Robert Froud, Tom Bjørkli, Philip Bright, Dévan Rajendran, Rachelle Buchbinder, Martin Underwood, David Evans, Sandra Eldridge
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​s12891-015-0825-6) contains supplementary material, which is available to authorized users.

Competing interests

TB, PB, DR, DE, RB and SE declare that they have no competing interests. RF and MU are also directors and shareholders of a company that provides electronic measurement services to health services researchers; notwithstanding this, they declare that they have no conflicts of interest. MU is a co-author on one of the trials included in this review.

Authors’ contributions

RF, RB, DE, MU, and SE conceived the study. RF managed the study, trained the review group, arbitrated reviewers decisions, performed the analyses, and wrote the first draft of the manuscript. TB, PB, and DR performed the review and abstracted data. All authors commented on the results, discussed the implications, and commented on successive drafts of the manuscript. All authors read and approved the final manuscript. All authors meet the ICMJE guidelines for authorship.



Low back pain is a common and costly health complaint for which there are several moderately effective treatments. In some fields there is evidence that funder and financial conflicts are associated with trial outcomes. It is not clear whether effect sizes in back pain trials relate to journal impact factor, reporting conflicts of interest, or reporting funding.


We performed a systematic review of English-language papers reporting randomised controlled trials of treatments for non-specific low back pain, published between 2006-2012. We modelled the relationship using 5-year journal impact factor, and categories of reported of conflicts of interest, and categories of reported funding (reported none and reported some, compared to not reporting these) using meta-regression, adjusting for sample size, and publication year. We also considered whether impact factor could be predicted by the direction of outcome, or trial sample size.


We could abstract data to calculate effect size in 99 of 146 trials that met our inclusion criteria. Effect size is not associated with impact factor, reporting of funding source, or reporting of conflicts of interest. However, explicitly reporting ‘no trial funding’ is strongly associated with larger absolute values of effect size (adjusted β=1.02 (95 % CI 0.44 to 1.59), P=0.001). Impact factor increases by 0.008 (0.004 to 0.012) per unit increase in trial sample size (P<0.001), but does not differ by reported direction of the LBP trial outcome (P=0.270).


The absence of associations between effect size and impact factor, reporting sources of funding, and conflicts of interest reflects positively on research and publisher conduct in the field. Strong evidence of a large association between absolute magnitude of effect size and explicit reporting of ‘no funding’ suggests authors of unfunded trials are likely to report larger effect sizes, notwithstanding direction. This could relate in part to quality, resources, and/or how pragmatic a trial is.
Additional file 1 Reviewers’ flowchart. A copy of the flowchart used by reviewers, guiding how to abstract standardised effect sizes and standardised SEs in PNG format. (PNG 198 kb)
Additional file 2 Characteristics of included studies. A table of characteristics of included studies in PDF format. (PDF 60 kb)
Additional file 3 Characteristics of excluded studies. A table of characteristics of excluded studies in PDF format. (PDF 69 kb)
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