Using Instrumental Variable (IV) methods to estimate the effect size in Colonoscopy Screening Trial (NordICC)

sensiblemed.substack.com

It is my pleasure to welcome this guest post by Prof Recht at Berkeley, CA. We have covered the NordICC trial of colonoscopy extensively— because it is big news, and because it matters. I recently interviewed the PI for Plenary Session (check it out on your podcast app). Here, we analyze it with instrumental variable methods. What the hell does that mean?

I don't understand authors that present results without confidence interval discussions. For example, authors might gush about their results showing that X had a 0.03 relative risk reduction without mentioning that the results are not statistically significant. If the results are not statistically significant, then why would one say we had a 0.03 relative risk reduction that wasn't statistically significant, rather than there was no statistically significant risk reduction.

While both statements are true, with the first statement there is anchoring around a relative risk reduction, with the second statement there is no anchoring.

Thanks for the post! I'm not sure that I understand the importance of what you are saying. It appears that in using this technique that you simply scaled the results by the percentage actually treated in the treatment arm. Isn't this the same as just analyzing those that were actually treated?

edited Oct 16, 2022I don't understand authors that present results without confidence interval discussions. For example, authors might gush about their results showing that X had a 0.03 relative risk reduction without mentioning that the results are not statistically significant. If the results are not statistically significant, then why would one say we had a 0.03 relative risk reduction that wasn't statistically significant, rather than there was no statistically significant risk reduction.

While both statements are true, with the first statement there is anchoring around a relative risk reduction, with the second statement there is no anchoring.

What am I missing?

Thanks for the post! I'm not sure that I understand the importance of what you are saying. It appears that in using this technique that you simply scaled the results by the percentage actually treated in the treatment arm. Isn't this the same as just analyzing those that were actually treated?