Understanding Risk - putting it into perspective

including websites, bc organisations, knowledge bases and instructional material.
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1266: count(): Parameter must be an array or an object that implements Countable
User avatar
Janette
Forum Legend
Posts: 15776
Joined: Tue Jun 13, 2006 10:23 am
Contact:

Postby Janette » Wed Sep 16, 2009 11:11 am

:bump:
Janette


Rosetta
Wise one
Wise one
Posts: 14
Joined: Sun Sep 03, 2006 11:26 am
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1266: count(): Parameter must be an array or an object that implements Countable

Postby Rosetta » Sat Apr 21, 2007 10:28 am

thanks for the great 'translation' of these really confusing concepts Janine!

User avatar
Janine
Founding Member
Founding Member
Posts: 4570
Joined: Wed Dec 07, 2005 5:04 pm
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1266: count(): Parameter must be an array or an object that implements Countable

Understanding Risk - putting it into perspective

Postby Janine » Fri Apr 20, 2007 5:28 pm

What do they mean when they say something increases your risk by X%? And how do you tell if that is significant? Perhaps this article might help to explain.

Absolute Risk and Relative Risk
Many reports in the media about the benefits of treatments present risk results as 'relative risk' reductions rather than 'absolute risk' reductions. This often makes the treatments seem better than they actually are. This leaflet tries to explain the difference between absolute and relative risk. This may enable you to make more informed decisions about whether to take a treatment or not.

What are absolute and relative risks?
Absolute risk is your risk of developing a disease over a time-period. We all have absolute risks of developing various diseases such as heart disease, cancer, stroke, etc. The same absolute risk can be expressed in different ways. For example, say you have a 1 in 10 risk of developing a certain disease in your life. This can also be said a 10% risk, or a 0.1 risk - depending if you use percentages or decimals.

Relative risk is used to compare the risk in two different groups of people. For example, the groups could be 'smokers' and 'non-smokers'. All sorts of groups are compared to others in medical research to see if belonging to that group increases or decreases your risk of developing certain diseases. For example, research has shown that smokers have a higher risk of developing certain diseases compared to (relative to) non-smokers.

A couple of examples may illustrate this better.
An example when talking about risks of disease. Say the absolute risk of developing a disease is 4 in 100 in non-smokers. Say the relative risk of the disease is increased by 50% in smokers. The 50% relates to the '4' - so the absolute increase in the risk is 50% of 4, which is 2. So, the absolute risk of smokers developing this disease in smokers is 6 in 100.

An example when talking about treatments. Say men have a 2 in 20 risk of developing a certain disease by the time they reach the age of 60. Then, say research shows that a new treatment reduces the relative risk of getting this disease by 50%. The 50% is the relative risk reduction, and is referring to the effect on the '2'. 50% of 2 is 1. So this means that the absolute risk is reduced from from 2 in 20, to 1 in 20.

Number needed to treat (NNT)
A figure which is often quoted in medical research is the number needed to treat - NNT. This is the number of people who need to take the treatment for one person to benefit from the treatment.

For example, say a drug company reported that drug x reduced the relative risk of developing a certain disease by 25%. If the absolute risk of developing the disease was 4 in 100 then this 25% reduction in relative risk would reduce the absolute risk to 3 in 100.

But looked at another way. If 100 people do not take the drug, then 4 will get the disease. If 100 people do take the drug, then only 3 people will get the disease. So, 100 people need to take the treatment for one person to benefit and not get the disease. So, in this example, the NNT is 100.

(A quick way of obtaining the NNT for a treatment is to divide 100 by the absolute percentage reduction in risk when taking the drug. So, another quick example. Say the absolute risk of developing complications from a certain disease is 4 in 20. Say a drug reduces the relative risk of getting these complications by 50%. This reduces the absolute risk from 4 in 20, to 2 in 20. In percentage terms, 4 in 20 is 20%, and, 2 in 20 is 10%. Therefore, the reduction in absolute risk in taking this drug is from 20% to 10% - a 10% reduction. The NNT would be 100 divided by 10. That is, 10 people would need treatment for one to benefit.)

Helping to decide about taking a treatment
The decision on whether to take a treatment needs to balance various things such as

what is the absolute risk of getting the disease to start with.
how serious is the disease anyway.
how much is the absolute risk reduced with treatment.
the risks or side-effects in taking the treatment.
how much does the treatment cost - is it worth it to an individual if the individual is paying, or is it worth it to the country if the government is paying.
It may help to look at a couple of examples:

Say your absolute risk of developing a certain disease is 4 in 1000. If a treatment reduces the relative risk by 50%, it means the 4 is reduced by 50%. Therefore, the treatment reduces the absolute risk from 4 in 1000 to 2 in 1000. Not really much in 'absolute' terms.

If it was a minor disease, one which you are likely to recover from, then you are not likely to bother to take the treatment.
If it is a fatal disease, you might consider taking the treatment - any reduction in risk may be better than none. However:
Say there was a 1 in 100 risk of developing serious side-effects from treatment. You are then not likely to want the treatment as the risk from serious side-effects is higher than the risk from the disease.
If there was no risk from the treatment, you might consider the treatment worthwhile.
If the treatment was very expensive:
then you may not be able to afford it and decide to take the risk without treatment
if the government is paying, it might decide not to fund this treatment as the reduction in absolute risk is not great and many people would need treatment to benefit one person.
On the other hand, say your absolute risk of developing a disease is 4 in 10 and a treatment reduces the relative risk by 50%. Your absolute risk goes down to 2 in 10 - quite a big reduction.

If it was a minor disease that you are likely to recover from, then you may still take the treatment if there was no risk of side-effects so as not to be troubled with the disease.
If it is a fatal disease, you a likely to definitely want treatment provided the risk of side-effects was much lower than the risk of getting the disease.

In summary
Treatments for medical conditions are often quoted in the press along the lines ..... "New treatment reduces your risk of x disease by 25%". However, although this sounds good, it usually refers to the relative risk. But the benefit really depends on how common or rare the disease is. A large reduction of relative risk for a rare disease might not mean much reduction in the absolute risk. For example, a 75% reduction in relative risk for something that has a 4 in a million absolute risk of happening brings the absolute risk down to 1 in a million.

When deciding on whether to take a treatment, ideally you should decide with your doctor if the reduction in the absolute risk outweighs the risks, side-effects and costs of treatment.
[From: ]

Also see:



Thank you for mentioning this the other night, Rosetta! It is something we need to understand, but is not often explained clearly.
Janine


[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1266: count(): Parameter must be an array or an object that implements Countable
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1266: count(): Parameter must be an array or an object that implements Countable

Return to “General Reference”

Who is online

Users browsing this forum: No registered users and 7 guests