Causality

Here's a thought for a lazy afternoon.

• Pornstars have lots of sexual intercourse
• Pornstars are often well-endowed in a genital-related manner (so they tell me)

Thus I can conclude from these two facts that more sex will enhance the size of your manhood. And I think I put it far better than most of the spam emails.

Unfortunately, while this logic is valid, it isn't true. We've missed the vital point that pornstars only generally get to be pornstars because they are well-endowed (in a genital-related manner). Their being well-endowed is in fact the cause of their being pornstars, and thus of getting the opportunity for lots of sexual intercourse, not the other way round.

Identifying causality is an enormous problem, especially as human beings often relate otherwise unrelated events (think "coincidence"). If two events occurring at the same time, it doesn't mean that one causes the other.

Another example:

• Autism often develops at 12-15 months (the figures may be wrong)
• The MMR jab is usually given at 12-15 months

Thus we can conclude that Autism causes the MMR jab. I suppose we could conclude that the MMR jab causes Autism. You'd be wrong to do either, however, without more research into the underlying causes of both. Despite lots of anecdotal evidence, "They gave my child the jab and he went autistic the next day," the simultaneous occurrence of MMR and autism is a coincidence.

And here, and also here is some really rather good evidence.