Monday, April 30, 2018

No Microbiome Santa Claus we cannot magically convert correlative studies into causal ones. And scientists dishing out medical advice about vaping based on such bad science is ridiculous.

Aaarrrrrrrg.  That is how I feel right now.

Many microbiome studies involve examining the microbiome in various samples and asking and answering "Are there differences in the microbiome between my sample types?".  This is a standard correlative analysis used in all sorts of areas of science. and it can be quite useful in many cases.

However, in most cases it is not OK to take information from a correlative study and infer that the microbiome was "changed" due to some factor that differed between the samples.  Generally this would only be possible to do in some sort of controlled experimental manipulation experiment.  But so so so many people make such inferences and I am going to highlight an example that relates to a new study of vaping and the microbiome.

There is a new paper on this topic and an associated press release:
Basically the researchers compared microbiomes in three groups of people who had different behaviors (some non smokers, some smokers, some papers vapers).  Note - they did not study people before and after vaping or smoking.  They compared different people who differed in these behaviors but also differ in 100s to 1000s of other things like diet, gender, age, activity, housing, childhood, and more.

And when they did comparisons in relation to the main variables of non smoker, smoker, vaper, they found some differences in microbiomes and some similarities.  Small study.  But potentially interesting.

However, the PR significantly misrepresents what they did and found. Here are some examples of wording I have a problem with:

Press Release:
  • "Vapers and non-smokers have the same flourishing gut flora."
    • OK this has nothing to do with the point of my post but they do not in any way show "flourishing" flora.
  • "whilst smokers have significant changes to their microbiome".  
    • No.  They show differences.  Not changes
  • Significant changes were found in the gut bacteria of the smokers, with an increase in the Prevotella bacteria which is linked to an increased risk of colon cancer and colitis.
    • Again.  No.  They show differences.  They do not know if they are changes since they do not know what these people had before smoking. And thus they cannot show "increases" either.
  • There was also a decrease in the presence of Bacteroides in smokers, a beneficial bacteria or probiotic.
    • No - no decrease shown.  And for that matter - not all Bacteroides are beneficial or probiotic. 
  • More investigation is needed but to find that vaping is less-damaging than smoking on our gut bacteria adds to the incentive to change to e-cigarettes and for people to use them as a tool to quit smoking completely.
    • Jesus #(@(@.  No.  They did not show this. 
  • This revealed significant changes in the gut bacteria of the faecal samples.
    • Again, no.