It's a pretty cool study. Basically, researchers measured how hot people drank their tea, and then ~10 years later looked at the difference that hot tea madepic.twitter.com/pOFEGNtMqP
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
Firstly, how did they collect tea heat preferences? It's not a variable you normally think about
The researchers got their subject to sit in a room, and gave them a cup of tea prepared at 75 degrees They put another cup of tea in front of them with a thermometer in it, and at cooling intervals asked the participants to take a sip and see if it was their preferred temppic.twitter.com/dTcdO2NoTQ
Now, I don't necessarily have a better way to do this - I mean, really, measuring how hot someone's tea is drunk? HARD - but this method has some clear elements of potential bias
However, this bias may not be that big an issue Why is that?
This one is pretty easy It's unlikely that the issues with tea heat measurement could've impacted group differences in cancer rates
This means that errors in grouping would've (probably) occurred equally across groups, and if anything biased the results towards the null
But there's another massive, glaring flaw that isn't touched on at all Reverse causality
To think about this, let's rewind The hot tea/cancer hypothesis goes like this: hot tea = damage to throat = cancer
But these people were measured at adulthood, and then followed over time The damage to their throat might have already happened So rather than the above sequence, we might see damage to throat = hot tea = cancer
Is this likely? Well, the hot tea drinkers were also older, smoked more, used opium more often, less wealthy, and drank more at baselinepic.twitter.com/kZYIQGXxY4
Given these confounders, is it likely that there was some reverse causality here?
(Forgot to answer the question above btw, it was all of the above - the effect applies equally to groups, probably a minimal impact, and biases towards the null anyway)
So, I'm just going to say it - yes, it's very hard in this situation to exclude reverse causality. There weren't any sensitivity analyses that really excluded it, so I think it's still pretty likely
This raises the last massive issue - residual confounding Note how the authors describe their findings vs the Daily Mailpic.twitter.com/iCvBZCoW0N
"Substantially strengthen the association" is NOT THE SAME AT ALL as "see their risk of gullet cancer rise by 90 percent" (Also, lol, gullet cancer is a great name)
Why are the authors so cautious Maybe it's because TEA DRINKING IS SUPER SOCIAL AND HARD TO UNPICK FROM CONFOUNDERS It's in caps because GODDAM IT I SAY THIS EVERY WEEKpic.twitter.com/GUAQyTAYof
We can't exclude residual confounding. Maybe people drink tea differently in different social situations. Maybe hot tea is more often served with alcohol. Maybe a single measure of how hot people drink their tea isn't that great a predictor 10 years later when they get cancer
Maybe there are a million factors you can never measure, and never control for, and thus it's really hard to know if this is causal or not Maybe
So the authors are cautious. They know that there's a decent chance that the heat of your tea has nothing to do with risk of esophageal cancer But the newspaper needs a story And so we get "hot tea causes cancer"pic.twitter.com/g6kancVrKs
So, let's recap: Large epi study showed 0.34% absolute increase in risk of cancer associated with drinking the hottest tea compared to cold tea, in large amounts, every day for 10 years Reverse causality and residual confounding remain an issue
Do we trust these results? Well, yes. The study was interesting, and well done Do we think hot tea = cancer?
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.