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Paeds Vivasprofessional-practice-and-evidence

Paeds Vivas · professional-practice-and-evidence

Clinical epidemiology and measures of effect — branching viva

Viva on computing and interpreting measures of effect in a paediatric study.

branching clinical structured oral3 min readVerification in progress

Target exams

RACP DCEMRCPCH ClinicalRCPSC Pediatrics
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Target exams

RACP DCEMRCPCH ClinicalRCPSC Pediatrics
Prompt
Journal club: you are given a case-control study of a common childhood outcome reporting an odds ratio of 4, alongside a randomised trial of a preventive therapy reporting a 50 percent relative risk reduction, a hazard ratio of 0.7, and a confidence interval whose lower bound crosses unity in some subgroups.

Opening (candidate)

I would approach these two papers by asking which measure of effect each design allows, and then checking whether the headline figure is the right one for that design. For the case-control study I would build the 2x2 table and compute the odds ratio myself, then ask whether the outcome is common enough to make reading it as a relative risk misleading. For the trial I would compute the absolute risk reduction and the number needed to treat from the event rates, read the hazard ratio alongside the Kaplan-Meier curve, and check whether the confidence interval crosses the null before trusting any of the figures. [7] [9]

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References9ShowHide
  1. [1]Sackett DL, Rosenberg WM, Gray JA, Haynes RB, Richardson WS Evidence based medicine: what it is and what it isn't BMJ, 1996.PMID 8555924
  2. [2]Laupacis A, Sackett DL, Roberts RS An assessment of clinically useful measures of the consequences of treatment N Engl J Med, 1988.PMID 3374545
  3. [3]Cook RJ, Sackett DL The number needed to treat: a clinically useful measure of treatment effect BMJ, 1995.PMID 7873954
  4. [4]Davies HT, Crombie IK, Tavakoli M When can odds ratios mislead? BMJ, 1998.PMID 9550961
  5. [5]Zhang J, Yu KF What's the relative risk? A method of correcting the odds ratio in cohort studies of common outcomes JAMA, 1998.PMID 9832001
  6. [6]Spruance SL, Reid JE, Grace M, Samore M Hazard ratio in clinical trials Antimicrob Agents Chemother, 2004.PMID 15273082
  7. [7]Greenhalgh T How to read a paper. Statistics for the non-statistician. II: Significant relations and their pitfalls BMJ, 1997.PMID 9277611
  8. [8]Altman DG, Bland JM Absence of evidence is not evidence of absence BMJ, 1995.PMID 7647644
  9. [9]Murad MH, Montori VM, Ioannidis JP, et al. How to read a systematic review and meta-analysis and apply the results to patient care: users' guides to the medical literature JAMA, 2014.PMID 25005654
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