O&G SAQs · Professional practice — Scholar role, research literacy and evidence-based practice
Research literacy — structured SAQ on appraising and interpreting a randomised trial (15 marks)
FRANZCOG-format structured SAQ on research literacy built on the ASPRE abstract: PICO, design, RoB 2 domains, odds ratio, confidence interval, P value and NNT interpretation, and GRADE certainty. Per-sub-part marking rubric included.
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FRANZCOGMRCOGABOG
Prompt
You are given the abstract of the ASPRE trial of aspirin for women at high risk of preterm pre-eclampsia. Preterm pre-eclampsia occurred in 1.6% of the aspirin group and 4.3% of the placebo group (odds ratio 0.38, 95% CI 0.20 to 0.74; P=0.004). (a) Frame the trial question in PICO. (2 marks) (b) State the design and the features of the analysis that protect against bias. (3 marks) (c) List the domains you would assess for this result with the Cochrane RoB 2 tool. (3 marks) (d) Interpret the effect estimate, including the number needed to treat. (4 marks) (e) Describe how GRADE rates the certainty of a body of evidence. (3 marks)
Mark scheme
Write short labelled points. Each sub-part is marked against the model answer below.
Reveal model answer and mark schemeShowHide
(a) PICO (2 marks)
- Population: women with singleton pregnancies at high risk of preterm pre-eclampsia.[1]
- Intervention and comparison: aspirin 150 mg per day versus placebo, from 11 to 14 weeks until 36 weeks.[1]
- Outcome: delivery with pre-eclampsia before 37 weeks.[1]
(b) Design and protection against bias (3 marks)
- Design: multicentre, double-blind, placebo-controlled randomised trial.[1]
- Analysis: intention-to-treat; results were materially unchanged in a sensitivity analysis accounting for the 152 women who withdrew consent and the 4 lost to follow-up.[1]
- Adherence: 79.9% of participants took 85% or more of the required tablets.[1]
(c) RoB 2 domains (3 marks)
- Bias arising from the randomisation process; bias due to deviations from intended interventions; bias due to missing outcome data; bias in measurement of the outcome; and bias in selection of the reported result.[4]
- The overall risk of bias is the least favourable judgement across the domains.[4]
(d) Interpreting the effect (4 marks)
- Odds ratio: 0.38 favours aspirin. An odds ratio should not be read as a risk ratio, because misinterpretation overestimates the effect, especially when events are common.[6]
- Confidence interval: 0.20 to 0.74 excludes 1. The 95% describes how often such intervals would contain the true value over many studies, not a 95% chance for this one interval.[2]
- P value: P=0.004 is not the probability that the null hypothesis is true.[2]
- NNT: the inverse of the absolute risk reduction, rounded up by convention.[3][7] Using the reported percentages (4.3% minus 1.6% = 2.7 percentage points), the NNT is 1 / 0.027 = 37.04, rounded up to 38.[1][7]
(e) GRADE (3 marks)
References7ShowHide
- [1]Rolnik DL, Wright D, Poon LC, et al. Aspirin versus Placebo in Pregnancies at High Risk for Preterm Preeclampsia. The New England journal of medicine, 2017.PMID 28657417
- [2]Greenland S, Senn SJ, Rothman KJ, et al. Statistical tests, P values, confidence intervals, and power: a guide to misinterpretations. European journal of epidemiology, 2016.PMID 27209009
- [3]Cook RJ, Sackett DL The number needed to treat: a clinically useful measure of treatment effect. BMJ (Clinical research ed.), 1995.PMID 7873954
- [4]Higgins JP, Savović J, Page MJ, Elbers RG, Sterne JAC Chapter 8: Assessing risk of bias in a randomized trial. Cochrane Handbook for Systematic Reviews of Interventions version 6.5 Cochrane, 2024.Source
- [5]Schünemann HJ, Higgins JP, Vist GE, Glasziou P, Akl EA, Skoetz N, Guyatt GH Chapter 14: Completing 'Summary of findings' tables and grading the certainty of the evidence. Cochrane Handbook version 6.5 Cochrane, 2024.Source
- [6]Higgins JP, Li T, Deeks JJ (editors) Chapter 6: Choosing effect measures and computing estimates of effect. Cochrane Handbook version 6.5 Cochrane, 2024.Source
- [7]Schünemann HJ, Vist GE, Higgins JP, Santesso N, Deeks JJ, Glasziou P, Akl EA, Guyatt GH Chapter 15: Interpreting results and drawing conclusions. Cochrane Handbook version 6.5 Cochrane, 2024.Source