Thursday, 30 August 2012

Prostate C and Fearmongering

Close up on now - raving on about prostate testing. Some guy is trying to get all the male viewers to go have a prostate test ... just in case. "I gat it, and got really scared, you should be scared too!" He's using bullying tactics to encourage men to go to the doctor. But if it saves lives, is that a bad thing?

I don't think they (Close Up) are making a good case. They point out that you are dumb not to get tested regularly because a "massive" 500 men a year are dying of prostate cancer.

Back-of-envelope - the male NZ population is about 2,200,000 so the annual chance of dying of prostate cancer (per year) is about 0.023%.

This means you'd have a 1.3% chance of dying from prostate cancer over about 60 years of adult life.

The advocate asserted that the $45 per visit to have the test "could be the best $45 you've ever spent" ... how likely is that? If I went to the doctor every month, that is $32000 over 60 years - the chance that was $32000 wasted is 98.7% isn't it?

But that's a bogus calculation ...the emphasis of the program is on the wrong stats. and on the wrong problem:

The stats:
... about a third of all the people who die in NZ, die of cancer.
Reducing cancer rates is a good national goal.

13% of (detected) cancer cases are prostate cancer - 2471/18615 cases.
(this won't include people who have non-terminal cancer who do not seek medical help.)

51 people a day are diagnosed with cancer, and there are 21 deaths.

So the 500 prostate deaths are 6.5% of all cancer deaths. (actually 7.1% = 561 deaths)
... if you are diagnosed, there is a 561/2471=23% chance you'll die of it - erk: roll a d4!
However, these are skewed by the people who waited long after symptoms to seek medical help.

And this is the real problem: the men are leaving it too long!

What the program has left off is how often one should get a prostate test to have a decent chance of detecting the cancer before it's too late.

So I looked it up: it is medically not recommended to give all men a prostate test (like we do with women and cervical or breast cancer).
While we now have some evidence that regular testing may prevent prostate cancer deaths, there are concerns that many men may be diagnosed and treated unnecessarily as a result of being screened, with a high cost to their health and quality of life. 
Men who show symptoms (broadly: trouble urinating - look it up) should certainly seek medical help though.

The Australia / New Zealand Urological society does suggest that men get the test once after they turn 40 - which can be a digital rectal exam (the doctor sticks a finger up your bum) and/or a blood test. This is to assess your risk for the next 15 or so years.

If you are going to the doctor anyway - the cost is going to be minimal: changing the cost-benefit calculation at the top in favor of having the test done.

So how scared should men be about prostate cancer? Not very.
I did mine a few years back.

Friday, 10 August 2012

Heliocentric experiments

I have recently been challenged to come up with an experiment that demonstrated the heleocentricity of the Earth-Sun system (that the Earth goes around the Sun) like experiments such as Foucault's Pendulum demonstrated the rotation of the Earth.

Demonstrating that you are accelerating is not as easy as Newton supposed. For instance, if you are sitting in a room and noticed that you were being pushed back in your chair, your cup slides towards you across the table and the lamp hangs from the ceiling at an angle, you could surmise that you are accelerating. OR that the room is tilting. OR that another mass has moved into position (somehow) to change the total gravitational field. OR that an invisible spirit is playing a joke on you. See what I mean?

There is nothing special, in physics, about heleocentricism - it is just another frame of reference. Its not even inertial since the Sun, with the entire solar system, accelerates around the local center of mass of the Galaxy and that about the local galactic cluster.

We only teach it in class because students seldom have the math to handle the arbitrariness of reference frames and because we favor, for philosophical reasons, those ideas that have the least amount of extraneous assumptions and fiddly bits.

So what am I to do?

Fortunately the phrasing of the challenge gives me a way forward ... you see, all the same arguments are valid for a spinning/not-spinning Earth. Classically we figure the Earth is spinning in the sense that we can show how coriolis and centrifgal effects vary over the surface. The spinning Earth is the least fiddly model that accurately accounts for what we can measure.

One of the consequences that leads to Foucault's pendulum also means it is easier to launch a satellite into a particular orbit if we have to account for the angular momentum of the Earth as it spins.

We have spacecraft that have visited the inner planets, and observation platforms about the Sun. In order to get them there, we have had to account for the orbital angular momentum of the Earth as it turns about the Sun. Here, then, is the experiment equivalent to the likes of Foucault's pendulum, that demonstrates heleocentricity in much the same way that other experiments demonstrate a spinning Earth.