So, I have an interesting question for #epitwitter and science fans
Is this study actually a randomized controlled trial (RCT)?
https://pubmed.ncbi.nlm.nih.gov/33150385/ pic.twitter.com/kaqkerQHvd
Epidemiologist. Writer (Guardian, Observer etc). "Well known research trouble-maker". PhDing at @UoW Host of @senscipod Email gidmk.healthnerd@gmail.com he/him
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So, I have an interesting question for #epitwitter and science fans
Is this study actually a randomized controlled trial (RCT)?
https://pubmed.ncbi.nlm.nih.gov/33150385/ pic.twitter.com/kaqkerQHvd
The question seems simple - the protocol describes a randomized trial comparing two forms of weightloss surgery (gastric bypass vs sleeve gastrectomy. They ran the trial, published one paper on the main outcome, and this is a second paper on bones specificallypic.twitter.com/RzQ1w5wb1M
Splitting up your big trial into two papers is a bit odd, but with the perverse incentives of academia (2 pubs is better than 1!) it makes sense so all good Except then we get to these paragraphspic.twitter.com/cIN5ECynIj
Looking at the final sample size in the paper, it turns out to be <50% of the final sample. So we've got a per-protocol analysis of <50% of the total sample that can't be done ITT because the data is missing 

pic.twitter.com/nzFGbv9xre
When did the authors decide to conduct this secondary analysis? Let's check the study registry!pic.twitter.com/8YhWy5WOBN
Looking at the history... Study started recruiting - Jan 2013 Study finished recruiting - Jan 2019 Secondary outcomes added to register - June 2018pic.twitter.com/gA964fhoWI
In other words, the study went for 5 1/2 years before adding these secondary outcomes, which might go a way towards explaining why >50% of the participants have missing data
Back to the original question - given that this is a per-protocol analysis of a subset of the study, with non-random selection on an outcome selected 5 years after the study began, is it fair to publish as an RCT?
I generally think RCTs are good, but we shouldn't treat RCT as being synonymous with good. This is a deeply problematic paper for lots of reasons, but they did randomize.
Yeh I'm on the fence here that's why I'm asking. They did indeed randomize, but also they broke the randomization for this subset so it's a bit tangled
My initial thought was that this would be more reasonably reported as a retrospective reanalysis of RCT data, because that makes clear the methodology used imo
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