Hello My Sweat Peas,

Mathspig has written for newspapers for 30 years. Aaaaah! The maths is frightening. One reason for starting this blog is to show mathpiggies everywhere why we need maths.

One area where we need maths concerns HEALTH STATISTICS. We make all sorts of decisions based on HEALTH STATISTICS.

It is not just the NUMBERS we must understand, but also the LOGIC.

Clear thinking. What do these numbers actually mean. Mathspig has even talked to HEALTH REASEARCHERS, who do not understand statistics. They use computer programs.

So this week Mathspig is applying LOGIC to Health Statistics. She’s looking at the Health Statistics that  Aren’t Good for Your Health.

One Health Statistic of interest involves genes and disease. Angelina Jolie had her healthy breasts removed because of the statistics involving breast cancer. But genes are NOT THE FULL STORY.

And Mathspig, who lervs pi, also loves chubby folk. The health statistics for fatties aren’t always as bad as some claim. See We’re All Gonna Die 2.

To learn a little about Health Statistics and LOGIC read on Sweet Pea.

Ciao

Mathspig

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.

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.

They bred lazy rats.

They bred active rats.

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.

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.

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.

This is a FALSE POSITIVE.

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:

As New Scientist pointed out:

The asked 8800 people about their health, lifestyle and television watching behaviour, and then followed them over the next six years, during which time 284 of them died. Among people who spent more than 4 hours a day in front of the TV, it found, the risk of their dying within the period of the study was 46 per cent higher than among those who watched less than 2 hours a day.

The error is confusing CORRELATION with CAUSATION. The risk might involve the sitting rather than TV. Or it could be that those who sit in front of TV longer are not well.

THIS IS A COMMON AND DANGEROUS ERROR INVOLVING HEALTH STATISTICS

Now that we have more screening tools we must be more cautious.

Angelia Jolie had her breasts removed because of testing positive for the BRCA 1 and BRCA 2 genes, which are linked to an increased risk of Breast Cancer.

This is her decision. Anyone facing breast cancer would seriously consider this option.

BUT, be wary if you face this decision.

Think of Asthma. If we started our research into asthma looking for asthma genes we would have found them.

Genes create a pre-disposition for Asthma (hence the correlation) but they do not cause asthma.  The dust mite, pollen, cat, dairy and other allergies cause asthma. If researchers had concentrated on genes alone our knowledge of asthma would be limited.

 Another study showed that 80% of prisoners in Australia smoke. Isn’t it obvious? Smoking causes criminal behaviour!!!!!

Not many children in Australia walk to school unsupervised or at all. The risks perceived by parents are out of proportion to the real risk. This is more to do with psychology than statistics.

It is a FAMILIARITY BIAS.

Parents are constantly shocked by images of  car accidents on the news (and kidnapped children. That’s another story.)

Likewise, parents in the UK worry about their children walking to school. But, as The Guardian noted, here are the stats for child pedestrian deaths in the UK.

In 2008 in England and Wales there were 1,471,100 girls aged between five and nine. The Office for National Statistics says 137 of them died from all causes. One was a pedestrian in a traffic accident. In 2010, there were no pedestrian deaths in this category.

We also tend to be more frightened by big numbers than little numbers.

This from the New Scientist.

In one study of this effect, people rated cancer as riskier when told that it “kills 1286 people out of 10,000″ than when told it “kills 24.14 people out of 100″

This makes living on the earth very dangerous as, according to the World Health Organization

approximately 156,000 people die a day. And don’t even think to look at your Star Sign. Obviously, 13,000 Geminis die each day and 13,000 Leos. And so on. For those concerned it was not their lucky day.

Too many death statistics are not good for your health either.

A link was assumed but after exhaustive tests no environmental cause was found.

See ABC abandons cancer scare building.

Tragically, independent events can cluster. One episode of Numb3rs explained this possibility very well. If you fire a machine gun at a barn wall and draw a circle around a group of bullet holes later that is a cluster. But don’t try this at home, mathspiggies. 

There is a great explanation of clustering here. Some Aussie road signs show clusters of IDIOTS!

Here is Ben Goldacre in a TED talk called Battling Bad Science.

Everytime a study finds this or that food is good or bad for you they usually make one huge error.

It’s called a BIASED SAMPLE.

Here is an example Real Men Eat Meat and Die

The study showed that “Men whose red meat intake put them in the top 20 per cent consumption band were 22 per cent more likely to die of cancer in the 10 years of the study, compared to men whose intake was in the lowest 20 per cent. For women, there was a 20 per cent increase in risk.”

The problem is big meat eaters tend also to be big drinkers, smokers, obese and the rest. This study has tried to separate out meat eating from other unhealthy lifestyle choices using the Cox Regression. Mathematical wizardry has produced these numbers but they don’t mean much.

If the study used a control group of drinking, smoking, obese vegans then compaing mortality rates over 10 years would be would be interesting. But where do you find half a million of them????????

Meanwhile any survey or study of a self-selecting group (eg. newspaper polls among readers) or a pre-existing group (eg. a church group, college students, yacht club, rock ‘n roll club) produces biased and therefore meaningless results.

eg. 9 out of 10 dentists who are paid to say they recommend Oral B toothbrushes is useless information, a study of paid jerks, really.

Look for a RTC or Randomised Controlled Trial. 

Any study that begins a ‘trial of college students found’ (eg. psychology trials) is a BIASED SAMPLE. Look at the lifestyle of college students. How many people in the general population wear beer hats to parties? If you asked 10 beer hat wearing college students their opinion on Oral B toothbrushes they might not even recall the purpose of a toothbrush!

Look for big randomised trials.

Fat people got no reason

Fat people got no reason

To live

They got big fat hands

Thunder thighs

They plod around

Puffin’ great big sighs

They got littler brains

They got damn iffy backs

They sit on their arses

Asking for heart attacks.

(With apologies to Randy Newman) 

 We are told there is an Obesity Epidemic as if you can catch obesity by standing beside someone packing a bit of cellulite.

If you have to be removed by a crane to get to hospital then you have a health problem. But obesity is presented in the media with such hysteria we could call it a NEGATIVE BIAS. The statistics are rarely questioned. And sometimes, these stats are not so damning.

Take diabetes and obesity statistics. Obesity increases the risk of diabetes.  True.

According to Australian Healthy Weight Week website, an affiliate of the Dieticians Association of Australia, 61% of Australian adults are overweight. Meanwhile, the Australian Institute of Health and Welfare puts the prevalence of diabetes in Aussie adults at 4.4% (all forms). Now wrap your head around this number. Even if all the 4.4% of  Aussies with diabetes  were overweight (they’re not), then 92.8% of fat people in Australia don’t have diabetes. But we still think fat people are evil.

They take up too much space

And breathe too much air

They stuff food in their faces

They don’t even care.

………………………………………

Make them fly freight on planes

They’re such a disgrace

 They should keep indoors

Let thin people run the place.

Fat people got nobody

Fat people got nobody

Fat people got nobody

To love them … (except me, I guess.)