Discover and read the best of Twitter Threads about #confounding

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Hey everyone! Here’s a #tweetorial on our new paper on why we often can’t make #causalinference using #distancetocare as an exposure or instrument! cc: @epiellie
There are 3 problems with #distancetocare as an exposure for estimating causal effects. Let’s walk through them.
The first problem that probably comes to mind is #confounding 🙀Choices about where to live and where to locate care facilities are complicated and depend on a lot of things we might not be able to measure (e.g. socioeconomic status).
Read 10 tweets
Edward Simpson, of Simpson's paradox, died last month at age 96.
telegraph.co.uk/obituaries/201…

Like all of us, I was taught #SimpsonsParadox by people who had not read what Simpson wrote:
jstor.org/stable/2984065

Then I read Simpson's paper and realized all the books were incorrect.
Simpson's example illustrates the distinction between confounders and colliders, but...

in 1972, Blyth failed to grasp the causal structure of Simpson's example and misrepresented it as confounding
jstor.org/stable/2284382

Most people read Blyth only, which perpetuated the error
So chances are that the #SimpsonsParadox you were taught is plain, extreme confounding

(all those cool graphs you have seen for Simpson's paradox just describe extreme #confounding)

when in reality Simpson's example is way more interesting.

More here
👇
academic.oup.com/ije/article/40…
Read 3 tweets
Randomization never ensures zero #confounding bias. It provides probabilistic bounds on confounding.

Therefore, by bad luck, the effect estimates from some perfectly conducted randomized #trials are substantially confounded. But we don't know which ones!

An eye-opening example:
In Denmark, 860 individuals were randomly allocated to either "intervention" or "control":
• No intervention was implemented
• Individuals were unaware of their allocation
• Mortality was higher in the intervention group with p=0.003

Keep this in mind when evaluating a trial.
Reference:
Vass M (PhD Thesis). Prevention of functional decline in older people. Faculty of Health Sciences, University of Copenhagen 2010, p.120.

Thanks to Mikkel Zöllner Ankarfeldt for bringing this example to my attention.
Read 7 tweets

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