Because my earlier post was rejected (as I included the attachment), I am resending my e-mail but including the link to the relevant paper I tried to attach:

https://annals.org/aim/article-abstract/1033260/distinguishing-case-series-from-cohort-studies) 

 

if someone wants a PDF of the paper, please contact me directly

 

thanks

 

ben

 

 

 

Thanks for your kind comments, Tom

By “manipulation” I am referring to any intent/capability of a researcher to determine (prospectively) health intervention assignment or environment in which study participant may find themselves. If we accept this, then a cohort study can also be classified as a trial (a prospective, matched study comes immediately to my mind).

 

Or, to simplify, assume you and I want to compare effect of treatment A vs B for disease D, but for whatever reason we cannot agree to run a RCT but we agree to run two separate cohort studies. So, you give Rx A to your group of patients, and I give RxB to my cohort (which we can then compare using matched design etc). So, I think we are dealing with a trial (or, two trials) according to the NIH definition of the trial (and according to definition of cohort studies in that classic paper by late Doug Altman and colleagues; see attached). (Note that the exposure in a cohort study can be determined by an investigator as an example #1 in the paper attached, or can be self-selected by the patients, as in the classic examples of the cohort studies assessing various outcomes in women who chose to use contraceptives. In the former example, cohort study can be classified as a trial, but not in the latter, I think).

 

Not sure if this provides a satisfactory explanation, but your point about difficulties what is a (clinical) trial is well taken (I think it took the NIH several years to come up with a definition I cited in my earlier e-mail and is still evolving…)

Thanks for ever interesting discussion

ben

 

From: Tom Jefferson [mailto:[log in to unmask]]
Sent: Saturday, January 25, 2020 10:37 AM
To: Benjamin Djulbegovic MD <[log in to unmask]>
Cc: David Nunan <[log in to unmask]>; [log in to unmask]
Subject: Re: Feedback - gauging what people mean by the word "trial"

 

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