• 1
    OCEBM Levels of Evidence Working Group. “The Oxford 2011 levels of evidence”. Oxford Centre for Evidence-Based Medicine. []. Accessed 30 January 2013.
  • 2
    Moher D, Hopewell S, Schulz KF, Montori V, Gotzsche PC, Devereaux PJ, et al. CONSORT 2010 explanation and elaboration: updated guidelines for reporting parallel group randomised trials. BMJ 2010;340:c869.
  • 3
    Higgins J, Green S, editors. Cochrane Handbook for Systematic Reviews of Interventions. Version 5.0.1. Chichester: The Cochrane Collaboration and John Wiley & Sons, 2008.
  • 4
    Blencowe H, Cousens S, Oestergaard MZ, Chou D, Moller AB, Narwal R, et al. National, regional, and worldwide estimates of preterm birth rates in the year 2010 with time trends since 1990 for selected countries: a systematic analysis and implications. Lancet 2012;379:216272.
  • 5
    Kenyon SL, Taylor DJ, Tarnow-Mordi W, Group OC. Broad-spectrum antibiotics for preterm, prelabour rupture of fetal membranes: the ORACLE I randomised trial. ORACLE Collaborative Group. Lancet 2001;357:97988.
  • 6
    Norman JE, Mackenzie F, Owen P, Mactier H, Hanretty K, Cooper S, et al. Progesterone for the prevention of preterm birth in twin pregnancy (STOPPIT): a randomised, double-blind, placebo-controlled study and meta-analysis. Lancet 2009;373:203440.
  • 7
    To MS, Alfirevic Z, Heath VC, Cicero S, Cacho AM, Williamson PR, et al. Cervical cerclage for prevention of preterm delivery in women with short cervix: randomised controlled trial. Lancet 2004;363:184953.
  • 8
    Haas DM, Caldwell DM, Kirkpatrick P, McIntosh JJ, Welton NJ. Tocolytic therapy for preterm delivery: systematic review and network meta-analysis. BMJ 2012;345:e6226.
  • 9
    The Editorial Team, Cochrane Pregnancy and Childbirth Group. About the Cochrane collaboration (Cochrane Review Groups (CRGs)) 2013, Issue 1. Art. No.: PREG. []. Accessed 10 January 2013.
  • 10
    Temple RJ. A regulatory authority's opinion about surrogate endpoints. In: Nimmo WS, Tucker GT, editors. Clinical Measurement in Drug Evaluation. New York: Wiley, 1995. pp. 322.
  • 11
    Cordoba G, Schwartz L, Woloshin S, Bae H, Gotzsche PC. Definition, reporting, and interpretation of composite outcomes in clinical trials: systematic review. BMJ 2010;341:c3920.
  • 12
    Egger M, Smith GD. Bias in location and selection of studies. BMJ 1998;316:616.
  • 13
    Williamson PR, Altman DG, Blazeby JM, Clarke M, Devane D, Gargon E, et al. Developing core outcome sets for clinical trials: issues to consider. Trials 2012;13:132.
  • 14
    Clarke M. Standardising outcomes for clinical trials and systematic reviews. Trials 2007;8:39.
  • 15
    Tugwell P, Boers M, Brooks P, Simon L, Strand V, Idzerda L. OMERACT: an international initiative to improve outcome measurement in rheumatology. Trials 2007;8:38.
  • 16
    Cooney RM, Warren BF, Altman DG, Abreu MT, Travis SP. Outcome measurement in clinical trials for Ulcerative Colitis: towards standardisation. Trials 2007;8:17.
  • 17
    Turk DC, Dworkin RH, Allen RR, Bellamy N, Brandenburg N, Carr DB, et al. Core outcome domains for chronic pain clinical trials: IMMPACT recommendations. Pain 2003;106:33745.
  • 18
    Schmitt J, Williams H, Group HD. Harmonising Outcome Measures for Eczema (HOME). Report from the First International Consensus Meeting (HOME 1), 24 July 2010, Munich, Germany. Br J Dermatol 2010;163:11668.
  • 19
    Devane D, Begley CM, Clarke M, Horey D, OBoyle C. Evaluating maternity care: a core set of outcome measures. Birth 2007;34:16472.
  • 20
    The COMET (Core Outcome Measures in Effectiveness Trials) initiative. []. Accessed 14 June 2013.