Sabina Vohra-Miller Profile picture
Apr 2 9 tweets 4 min read Read on X
In science & esp medicine, risk is a tricky thing to contend with - besides of course being a mathematical one - and involves many considerations in order to have a more fulsome understanding.

In this post @LizMarnik and I attempt to explain these concepts. 1/9 Let’s talk risk  What is relative vs absolute risk? What is cumulative risk? Why do these terms matter? And how do these impact our lives?
In simple terms, risk is the probability of an event occurring. In statistical terms, the risk of an event occurring is simply defined as its probability.
2/9 WHAT IS RISK? In simple terms, risk is the probability of an event occurring. In statistical terms, the risk of an event occurring is simply defined as its probability. Absolute risk of a disease is your risk of developing the disease over a time period. Relative risk is used to compare the risk in two different groups of people. What does this mean?
Take a fictitious disease - AhCrap. Risk of dying due to this is 2/million & using GoodStuff tx can reduce risk to 1/million.
While relative risk reduction is 50%, only one less person out of 1M w AhCrap are saved by GoodStuff, making absolute risk reduction fairly small.
3/9 ABSOLUTE VS RELATIVE RISK Take a fictitious disease, say Disease AhCrap. The risk of dying due to AhCrap is two in a million - ie, for every one million people who suffer from AhCrap and are not treated, two out of these one million people will die. Let's say we have a way to treat this AhCrap disease, using GoodStuff treatment. This treatment can reduce the risk of dying from two in a million to one in a million. Because the risk of dying decreased from two in a million to one in a million, the relative risk decreased by 50%. However, the absolute risk only changed from 2/1,000,000 to 1/1,...
Because the risk of dying decreased from two in a million to one in a million, the relative risk decreased by 50%.

However, the absolute risk only changed from 2/1,000,000 to 1/1,000 000, that is, a difference of 0.00005%.
4/9 Pictograph showing the numbers described in previous slide
A few other things to consider, such as:
what the likelihood of the risk occurring is and what the risk-benefit analysis including downstream impacts are.

The examples in this slide demonstrate these points to help put overall risk into context.
5/9 There are a few other things to consider to put these into context: Using the same example as before, say there is a Foodltem that can prevent AhCrap disease from occurring if you eat it daily. In fact, this food can reduce the lifetime risk of AhCrap from happening by 50%. But actually, the risk of ever developing AhCrap disease itself is only one in 1 million people. So even though this Foodltem can cause a significant reduction in AhCrap occurring, it means every single person would need to eat this food item daily to change the risk of developing AhCrap from 1 in 1 million to 0.5 in 1 m...
Changing gears, let’s talk about cumulative risk, which is the combined risk from multiple exposures or behaviors over time.

This requires several pieces of information, such as time period, how many exposures, risk assoc w each & how other behaviors impact the likelihood.
6/9 Cumulative risk is the combined risk from multiple exposures or behaviors over time. Let's say we are trying to determine the cumulative risk of Badinfection causing issue TerribleOutcome if people can be infected with it multiple times throughout their lifetime. To do this you need to have estimates of the following: 1. What is the likelihood of this outcome? 2. Does each subsequent infection have the same individual risk? 3. Do treatments, behaviors or other things increase or decrease this risk? If they do, how much of an impact is it having on likelihood? 4. How long is the time period ...
Take this example: risk of TerribleOutcome after the first time one has BadInfection is 2 in 100 or 2%. Risk after each subsequent infection is 1 in 100 or 1%.
Cumulative risk in this example of person having TerribleOutcome over lifetime, i.e. a 15 year period is 3.95%
7/9 To make this more simple let's make some assumptions. Let's assume: • Badinfection happens on average once every 5 year. • No treatments or vaccine makes TerribleOutcome less likely. • Individual in question is 70 years old and may live to 85 years. • Risk of TerribleOutcome after the first time one has BadInfection is: • 2 in 100 or 2% • • Then the risk of TerribleOutcome after each subsequent infection is: • 1 in 100 or 1%. That means there could possibly be up to 3 infections for this person so what the cumulative risk of a person experiencing TerribleOutcome over this person's lifetime,...
So as we can see in this situation, while the individual risk of a subsequent Badinfection may infact be lower than the first infection, the cumulative risk of developing BadOutcome is higher with each additional infection.
8/9 Image
Understanding these can help you make informed decisions.

Putting into context how likely risk is, what impact of the risk is, what overall risk-benefit analysis is & downstream impacts are all important considerations when assessing & evaluating risks + decisions.

9/9 Understanding difference between relative & absolute risk can help you make informed decisions as you evaluate the risks and benefits of different decisions you are making. There may be interventions that have a large relative risk reduction, but absolute risk - & ultimate difference it may make to your life - might be miniscule. On the other hand, sometimes even if change in absolute risk is small, intervention may still be worth it depending on the overall risk-benefit equation. Similarly, there may be situations where absolute risk of an outcome is lower with each repeated occurrence; ho...

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Sabina Vohra-Miller

Sabina Vohra-Miller Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @SabiVM

Feb 26
A week ago, a new paper was published evaluating the safety of Pfizer, Moderna & AstraZeneca vaccines. Unfortunately, the media’s response with sensational headlines has been both irresponsible & misleading.

Here is a deep dive I did with @LizMarnik & @niniandthebrain

🧵 1/10 COVID VACCINE SAFETY Benefits outweigh risks
Study in question:

2/10 sciencedirect.com/science/articl…
Article https://www.sciencedirect.com/science/article/pii/S0264410X24001270
This study evaluated the rate of several rare events in the 42 days post vaccination compared to pre-COVID rates

The study looked at 99,068,901 individuals that represented over 242 million doses of Pfizer, Moderna or AstraZeneca.
3/10 RARE ADVERSE EVENTS EVALUATED This study evaluated the rate of the following events in the 42 days post vaccination compared to pre-COVID rates: : Guille dissemisated ence/caloyelitis (ADEM) • Transverse myelitis (T™) • Bell's Palsy. • Febrile and generalized seizures • Cerebral venous sinus thrombosis (CVST) • Thrombocytopenia • Pulmonary embolism (PE) • Splanchnic vein thrombosis (sVT) • Myocarditis • Pericarditis The study looked at 99,068,901 individuals that represented over 242 million doses of Pfizer, Moderna or AstraZeneca. @Niniandthebrain x @UnambiguousScience x @ScienceWhizLiz
Read 10 tweets
Jan 21
Does Long Covid alter the immune system?

New evidence suggests this may indeed be the case.

Study summary in collaboration with @LizMarnik
1/7 Image
This is the study we attempt to summarize:


2/7 nature.com/articles/s4159…
Research is slowly starting to find out what processes may be behind some of the symptoms those with long COVID experience.  Image shows screenshot of actual article
Samples were collected via a prospective observational study that enrolled individuals with prior SARS-CoV-2 infection with and without long COVID symptoms
3/7 Participants were enrolled in a prospective observational study that enrolled individuals with prior SARS-CoV-2 infection with and without long COVID symptoms.  Samples were collected from participants at 8 months post infection before any participants were vaccinated or reinfected. Results were compared between those with long COVID symptoms to those without.
Read 7 tweets
Jul 30, 2023
Two new Canadian studies demonstrating the efficacy of masks.

These studies show that mandatory masking, esp during periods of high respiratory viruses in the community, can result in reductions in absenteeism, prevent infections and deaths & reduce economic burden. 🧵 1/9 2 new Canadian studies demonstrating efficacy of masks
First study by @NishaOttawa , @DrKevinSchwartz , @KevinAnBrown et al.

This study examined whether school-based mandatory masking policies were associated with reduced educational disruptions due to COVID-19 and other respiratory viruses 2/9 This study examined whether school-based mandatory masking policies were associated with reduced educational disruptions due to COVID-19 and other respiratory viruses
A total of 77 640 students from 205 schools were included:

166 were elementary schools, of which 60 (36.1%) had mandatory masking policies
39 were secondary schools, of which 12 (30.8%) had mandatory masking policies 3/9 The study included student and staff absenteeism in public elementary and secondary schools in Ottawa from March 21 to May 19, 2022, using a difference-in-differences design.  During this time, there was co-circulation of COVID-19, Influenza and RSV.  Given the incubation of COVID-19, a wash-in period was included, where masking was assumed to have no association on day 1, then increasing by 10% per school day to reach the full result after 10 school days.  A total of 77 640 students from 205 schools were included:  166 were elementary schools, of which 60 (36.1%) had mandatory masking poli...
Read 9 tweets
Jun 16, 2023
A thing that invariably shocks a lot of people is when I say I don’t trust most science-related books or documentaries.

So, I want to explain why, and situate it within one of my all-time fav things: evidence. 🧵 /1
What constitutes good evidence?

First, all data is not created equally.

When it comes to publications, most people, including academics, tend to read the abstract and perhaps skim quickly through the data. /2
But that doesn’t tell you how robust or valid the study and results are, ie, whether the design, conduction and methodology are able to successfully prevent systematic errors or bias. /3
Read 15 tweets
Feb 5, 2023
New study comparing myocarditis due to Covid-19 vaccines vs infections.

There was a markedly higher risk of heart failure and death for myocarditis associated with Covid-19 infections compared to Covid-19 vaccination.
1/4 new study comparing myocarditis due to covid-19 vaccines VS
Subanalysis of age 12-39 & no comorbidities showed Covid-19 infection related myocarditis was assoc with 5.8x higher risk of heart failure or death vs vaccine related myocarditis.

Confirms Covid-19 related myocarditis far less severe with vaccinations than with infections.
2/4 subanalysis looking specifically at those aged 12-39 (highes
Beware those who compare the numbers of the events - we do not have the denominator for any of the groups, so this study cannot be used to discern incidence or rate. Those with no scientific background will use this data nefariously. 3/4

bmjmedicine.bmj.com/content/bmjmed… Beware those who compare the numbers of the events - we do n
Read 4 tweets
Feb 3, 2023
Part 1 of the series on Covid-19 vaccinations and pregnancy, fertility and breastfeeding.
This one focuses specifically on the updated data we have in pregnancy - from the impact of infections to safety and benefits of the vaccine. 🧵1/11 Covid-19 vaccine pregnancy ...
Risk of severe outcomes due to Covid-19 infection in pregnancy continue to be high for the pregnant person.
Studies show these risks are highest for those unvaccinated. 2/11 Covid-19 infections in preg...
There are also considerable risks to the fetus/baby due to Covid-19 infections in pregnancy.

Studies show that risk of stillbirth and neonatal mortality highest in those unvaccinated. 3/11 There are also considerable...
Read 12 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

:(