Investigators are reviewing electronic health records to assess the safety profile of a newly approved oral anticoagulant. Specifically, they are comparing the incidence of major gastrointestinal (GI) bleeding among patients prescribed this new medication versus those prescribed warfarin.
Initial unadjusted analysis reveals a statistically significant elevation in major GI bleeding events among users of the novel anticoagulant (, ).
During peer review, the investigators are asked to account for concurrent medications. They subsequently stratify their patient sample based on concurrent nonsteroidal anti-inflammatory drug (NSAID) use.
The re-analysis yields the following results:
- Subgroup actively taking NSAIDs: ()
- Subgroup not taking NSAIDs: ()
In their revised manuscript, the investigators state: "Our findings indicate that concurrent NSAID use acts as an effect modifier that synergistically elevates the risk of major GI bleeding when combined with the novel oral anticoagulant."
Which of the following best describes the primary methodological flaw in the investigators' interpretation?
- They misinterpreted a confounding variable as an effect modifier, given that the association is eliminated upon stratification.Answer
- BThey selected an incorrect inferential statistical test by utilizing a chi-square analysis instead of an ANOVA for categorical bleeding outcomes.
- CThey failed to identify a cytochrome P450-mediated drug interaction that fundamentally alters the anticoagulant's pharmacokinetic profile.
- DThey overlooked the epidemiological principle that positive predictive values for adverse events change with the background prevalence of NSAID use.
- EThey failed to recognize that concurrent prescription of these medications is an absolute contraindication, which inherently invalidates the study cohort.