I have posted an answer to your question below. Please let me know if
you have further questions or if I can clarify this for you,
especially if you have questions related to a specific procedure.
1. Natural frequencies
A frequency is a measurement of how often something happens. It can be
thought of as similar to a rate. For example, if there are 100,000
people living in a town and each year 20 get the chicken pox, the
frequency is 200 per 100,000 per year.
A natural frequency is the frequency of some event or disease in the
general population. For example, the example above is a natural
frequency of chicken pox, with no vaccine. If a vaccine were given,
the actual frequency of chicken pox would go down (less people would
get it) maybe to 10 per 100,000 per year and be less than the natural
frequency. In other words, an intervention of some kind may change the
frequency to be something other than the natural frequency. You can
imagine a town with radioactive waste will have a frequency of cancer
that is higher than the natural frequency, and a country that uses
2. Absolute risks
There are different kinds of risks in medical statistics
(epidemiology). An absolute risk is the true probability of some event
affecting someone in a particular population. For example, the risk of
a heavy smoker getting lung cancer might be 10%. This is different
than a relative risk. A relative risk is a comparison between two
risks. For example, if a non-smoker has a 1% chance of getting cancer,
the heavy smoker's relative risk is 100. As you can see, if we look at
relative risks we may get very different numbers compared to absolute
risks. Sometimes researchers or companies will report relative risks
(or a difference between risks, called a risk reduction) because they
sound more dramatic. For example, they will say that a using a certain
medication will reduce your risk of heart attack by 50%. This sounds
amazing, but if the risk of heart attack WITHOUT taking the medicine
is very small (the absolute risk is very small), then a 50% reduction
is not very much. It might only be a change from 1/2% to 1/4% or less.
In general, it is more accurate to look at absolute risks when
deciding on a procedure or a treatment, because it tells you the true
probability of something happening.
I hope this helps,
RMH
Absolute and relative risk
http://info.cancerresearchuk.org/cancerandresearch/risk/communicatingrisk/absoluteandrelativerisk/
Weighing treatment pros and cons
http://www.breastcancer.org/treatment_stats.html |
