Spot the logical fallacy

This week I've spotted a couple of daft articles and letters that demonstrate the general lack of critical thinking around today.

The first one was in the National Trust magazine. There were a couple of letters in response to a recent NT article on gardening by the phases of the moon. On the face of it, it sounds a bit weird, but should be testable.

I found a couple of interesting resources on moon-planting. One is a calendar that advises which things to plant according to the phase of the moon and other astrological signs.

Here's the letter

I was interested in the article on planting by the moon. This is something I've been doing for years - and have been teased because of it! But I swear by the method Ed Ikin described, and to prove it, this year I planted some runner beans before the end of April - although the new moon was to be later in May. Result: only two beans germinated. I planted a second batch on 5 May and within less than a fortnight had 90 per cent germination. The best method is to cut the inside of a kitchen roll into three, fill with soil and pop a bean into each. The whole lot can then be planted with little disturbance to the roots.

Apart from the obvious point that the second batch were planted at a later date (probably warmer condition, though it's hard to tell in this country), it's so typical that someone will try a particular technique, find it works and then prescribe the success to that technique without considering the other factors at play.

The other item was in my local paper, The Weston Mercury. It concerned the sad story of a couple who have both recently contracted cancer. She was diagnosed with Non-Hodgkins lymphoma in November 2007 and he was diagnosed with leukaemia in February 2008. It's an awful thing to happen to anyone - my dad died of cancer, but the reason for the story being in the paper was that they claim that their illnesses result from being caught up in the Asian tsunami in 2004.

They say they can

trace their ill health back to the day when they were forced to shelter on an iron roof after the wave struck.

They

asked doctors if there could be a link - they told her it was possible but nothing could be proved

The wife says

I'm convinced it has something to do with it. Before the tsunami I was fit and healthy, but afterwards I was having five or six weeks off work at a time...It was like I had my immune system lowered. I would get ill all the time

 

The husband says

I'm a bit more scientific about it, but the tsunami is the only common factor. Everything has gone downhill since that date and we have not been able to pull ourselves out of it

It's a weird kind of non-story. They don't appear to be trying to gain anything from the story, just stating what they think is to blame for their illnesses.

Maybe cancer can be triggered by stress, maybe not. I'm not doctor (well, not that sort of doctor). The point in both these cases is that people seem to be happier if they can find some pattern or reason for what happens to them or around them. I'm there are more than one logical fallacy in each of these cases, but they definitely seem to come under post hoc ergo propter hoc, i.e. assuming that a temporal relationship between two event implies a causal relationship.