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  "path": "/t/decision-analysis-in-clinical-guidelines-net-benefit-nnt-nri/28682#post_5",
  "publishedAt": "2026-04-01T01:19:50.000Z",
  "site": "https://discourse.datamethods.org",
  "textContent": "Thank you for taking the time to catch me up. Also thank you for the derivation. It is nice to see things written in terms of probabilities rather than the acronyms.\n\nI still wonder how one is to estimate P(ASCVD|No Tx), because the pooled cohort equations provide P(ASCVD). I.e., from the corresponding 2013 ACC/AHA guidelines [1]:\n\n“A variable representing lipid treatment was considered but not retained in the final model because lipid therapy was relatively uncommon in the cohorts and statistical significance was lacking.”\n\n  1. Goff Jr, David C., et al. “2013 ACC/AHA guideline on the assessment of cardiovascular risk: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.” _Journal of the American college of cardiology_ 63.25 (2014): 2935-2959.\n\n\n\nI guess because lipid treatment was relatively uncommon, they assumed it was not present. They should have at least then removed all cases that received lipids, but I’m not sure whether that would have biased the model.\n\nOverall, as described in [2], the data used to estimate the pooled cohort equations were from (I guess this is obvious given the name) cohort studies. I think the real quantity that’s needed in a decision though is P_trial(ASCVD|No Tx), also called P(ASCVD|do(No Tx)). I think actually RRR = (P_trial(ASCVD|No Tx)- P_trial(ASCVD|Tx))/P_trial(ASCVD|No Tx), right? We don’t estimate this with observational data, because then there is confounding by indication—ie what if the people who took statins were healthier? Is it really\n\nRRR * P_**cohort(**ASCVD|No Tx)?\n\nIf so, to combine ASCVD risk estimated with cohort with a risk reduction statistic from a trial seems like it might create a mismatch.\n\nIt would be the case, assuming that the authors of the graphic above were thinking of using the pooled cohort equations to estimate P(ASCVD|No Tx) (or P(ASCVD)), and not the trial that was used to compute ARR (this would be a better idea, IMO), or some other calculator. In most guidelines though, the pooled cohort equations are used, and as far as I know, most people at the point of care would be using those equations to derive the ASCVD risk.\n\nGiven that all this still works out, I have to think a lot more about NNT and NND then somehow being used to approximate the expected utility problem.",
  "title": "Decision Analysis in Clinical Guidelines: Net Benefit, NNT, & NRI"
}