Posts Tagged ‘common errors in health statistics’


1. Why bother?

June 14, 2013

The most annoying health statistics are based on small study groups. 

 Picture 1

eg. 9 out of 10 dentists recommend this toothbrush. Oral B as it turns out.

In maths we call this for obvious reasons a SMALL SAMPLE SIZE.  This may not be a problem when buying a toothbrush, but what if they are trying to sell you – sticking with thedentist theme – a $5,000 procedure that breaks your jaw and resets it to improve your bite?

Where are the numbers? Has there even been any research? Or a large-scale survey about this procedure? Are people happy with this procedure? Did it even work?

You do not want to make a health decision based on a study involving a SMALL SAMPLE. From the above ad, a sample of 1, dentists are a hot date. You may not want to put your faith in this statistic.


2. Rats and Stats

June 14, 2013

Often the alarming results of health studies published in the media are based on rats. Any study of rats gives us a insight into possible links to human health, but further studies are needed.

eg. Couch Potatoes May Be Genetically Predisposed to Being Lazy, Rat Study Suggests. The study by Frank Booth, a professor in the MU College of Veterinary Medicine was able to selectively breed rats for extreme activity or extreme laziness. They say these rats indicate that genetics could play a role in exercise motivation, even in humans.

lazy rat

They bred lazy rats.

sports rat

They bred active rats.

ratin a hat

They even bred rats in hats.


Rats DO NOT THINK like humans. There is no rat walking around asking ‘does my butt look big in this?


‘Even if rats experience the same disease they do not benefit from the PLACEBO EFFECT. Give a rat a sugar pill, it is just a sugar pill. But for humans a sugar pill can be 50% of the drug efficacy. Easily.

Health studies involving rats just point to an area of further research.

eg. In the 1970s rat studies suggested that artificial sweeteners caused bladder cancer. There was panic. Outrage. Hysteria. Eventually it all settled down. Further studies could not establish a link to cancer in humans. More info National Cancer Institute.

The results of rat studies are only relevant to those who hang out with lab rats namely the researchers.

There is no maths term to describe this statistical error. I’ll simply call it RATTY RESEARCH.


3. Stuff Ups 1

June 14, 2013

You go to the doctor with lower back pain.

bad back

The doc recommends an MRI scan. A problem is identified and an operation, perhaps, recommended. But here is the problem. The back problem identified in the scan may not be the cause of the pain.

Risks: health screening

In maths this is called FALSE ATTRIBUTION.

You get all the pain – financial and physical – but no gain.

You will find a very interesting discussion of this problem The Health Report, Radio National, ABC.

Dentists suffer a higher incidence of lower back pain … Maybe from prancing around in towels in front of mirrors. Wait. That was only a small sample of 10 paid dentists.

No conclusion can be drawn.


4. Stuff Ups 2

June 14, 2013

All medical tests are subject to a % error.



This may not be a problem if you are advised to, say, take more Vitamin D to correct the problem you don’t have. But if you are being advised to undergo major surgery, a second test is advisable.

As statistician Michael Blastland explained in Everyday risks: when statistics can’t predict the future (The Guardian 9 JUN 2013):

False positives are common for the simple reason that if you test a million healthy people, even with a 99% accurate test, you will still have 10,000 wrong results. And that’s not including human error. Hopefully, you will not experience one of these:

x ray