title: 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.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Clinical Trials Unit, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK. r.froud@warwick.ac.uk.|Norge Helsehøyskole,, Campus Kristiania, Prinsens Gate 7-9, 0152, Oslo, Norway. r.froud@warwick.ac.uk.
authors.forename: Robert
authors.initials: R
authors.lastname: Froud
authors.affiliation: Norge Helsehøyskole,, Campus Kristiania, Prinsens Gate 7-9, 0152, Oslo, Norway. tomeirikkjeldsen87@yahoo.com.
authors.forename: Tom
authors.initials: T
authors.lastname: Bjørkli
authors.affiliation: European School of Osteopathy, The Street, ME14 3DZ Boxley, Maidstone, UK. philbright@eso.ac.uk.
authors.forename: Philip
authors.initials: P
authors.lastname: Bright
authors.affiliation: Norge Helsehøyskole,, Campus Kristiania, Prinsens Gate 7-9, 0152, Oslo, Norway. devanrajendran@eso.ac.uk.|European School of Osteopathy, The Street, ME14 3DZ Boxley, Maidstone, UK. devanrajendran@eso.ac.uk.
authors.forename: Dévan
authors.initials: D
authors.lastname: Rajendran
authors.affiliation: Monash Department of Clinical Epidemiology, Cabrini Institute and Department of Epidemiology and Preventive Medicine, Monash University, Suite 41, Cabrini Medical Centre, 183 Wattletree Road, Malvern, 3144, Melbourne, Victoria, Australia. rachelle.buchbinder@monash.edu.
authors.forename: Rachelle
authors.initials: R
authors.lastname: Buchbinder
authors.affiliation: Clinical Trials Unit, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK. m.underwood@warwick.ac.uk.
authors.forename: Martin
authors.initials: M
authors.lastname: Underwood
authors.affiliation: Clinical Trials Unit, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK. dwe@backpainclinic.co.uk.|Norge Helsehøyskole,, Campus Kristiania, Prinsens Gate 7-9, 0152, Oslo, Norway. dwe@backpainclinic.co.uk.
authors.forename: David
authors.initials: D
authors.lastname: Evans
authors.affiliation: Barts and the London School of Medicine and Dentistry, Queen Mary University of London, 58 Turner Street, London, E1 2AB Whitechapel, UK. s.eldridge@qmul.ac.uk.
authors.forename: Sandra
authors.initials: S
authors.lastname: Eldridge
mesh_terms: D016265:Conflict of Interest; D019317:Evidence-Based Medicine / Q000191:economics / Q000592:standards; D006801:Humans; D055811:Journal Impact Factor; D017116:Low Back Pain / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D017712:Peer Review, Research; D010506:Periodicals as Topic / Q000191:economics / Q000592:standards; D017410:Practice Guidelines as Topic; D017594:Publication Bias; D016032:Randomized Controlled Trials as Topic / Q000191:economics / Q000592:standards; D012107:Research Design / Q000592:standards; D012109:Research Support as Topic / Q000592:standards; D018401:Sample Size; D013997:Time Factors; D016896:Treatment Outcome