Thread by @NidaQadirMD

Still getting the hang of Twitter chatting but...
A2 - start with brushing off your journal club #skillz! There are so many points to make here in terms of identifying confounders and bias, but I'll start w/ one I get asked about a lot - immortal time bias! #ATSChat

https://twitter.com/atsearlycareer/status/1334184302158901251

A2 - Immortal time = period of time during which, due to study design, the study outcome cannot occur. Occurs when there’s a difference between the timing of entrance into the study cohort & timing of the exposure. Exposure = the treatment being assessed. #ATSChat (2)

A2 - This can bias the results in favor of the exposure (ie treatment) group ➡️ immortal time BIAS. #atschat (3)

A2 - Example:
Population = critically ill adults w/ COVID-19
Exposure = burgers
➡️ Dose = 1 burger TID x 24 hrs – must get 24 hrs of burgers to be in treatment group
Outcome = hospital mortality
#ATSChat (4)

A2 - Because of time bias, patients who die within 24 hrs are in the “untreated” group ➡️ gives a spurious survival advantage to the treated group. #ATSChat (5)

A2 - Also - let’s say burgers require GI approval & can only be administered in the ICU ➡️it may take a day or 2 for a pt to get burgers, especially if there’s a shortage of ICU beds (ie pts are critically ill but boarding in ED). #ATSChat (6)

A2 - Time to exposure is even longer ➡️pt has to live even longer (time it takes to get to ICU & get GI approval + 24 hrs of burger administration) to be considered in the treatment group #ATSChat (7)

A2 - In this diagram, it looks like 75% of untreated patients died vs 25% of treated patients. In reality, if you look at just the patients who actually lived long enough to have a chance of getting the treatment, there was only 1 death in each group. #ATSChat (9)

A2 - Another obvious bias NOT related to immortal time - burgers can’t be administered to patients who aren’t conscious or otherwise can’t take PO ➡️ these are probably sicker patients who end up in untreated group. #ATSChat (10)

A2 - this example is silly, and I really want a burger, but this happens all the time - ie - a patient must be on a particular med x 24 hrs to be in the treatment group...a patient must be able to take PO...(11)

...and after so much burger talk, I had to get one. Just as effective as #HCQ for treating #COVID19, but much more delicious.