I have a cold (and they're worse than you remember when you're well). Throughout the nation, homeopaths and self-declared nutrition therapists are celebrating. More importantly, I know that there is almost nothing I can do, except sit it out, and wait. Vitamin C will shave a few hours off it, at high doses, like 7g a day, which I can happily live without.

Although literally anything I try will appear, to me, to work: because unless I'm seroconverting with HIV (not that I'm prone to hypochondria) I will get better anyway. This is the natural history of the illness, and it's true with most things. When your back pain is at its worst and you visit your doctor - or your friendly local spoonbender - it's bound to get better, because these things come in cycles, or as statisticians say, they "regress to the mean". You can look at regression to the mean mathematically, if you like. On Bruce Forsyth's Play Your Cards Right, when Brucey puts a three on the board, the audience all shout: "Higher!" because they know the odds are that the next card is going to be higher than a three. "Do you want to go higher or lower than a jack? Higher?" "Lower!"

So I could take homeopathy. Or I could, equally stupidly, harass my GP for antibiotics, even though they are ineffective in treating a viral cold.

In one study, prescribing antibiotics rather than giving advice on self-management for sore throat resulted in an increased overall workload through repeat attendance. If a GP prescribed antibiotics for sore throat to 100 fewer patients each year, they calculated: 33 fewer would believe that antibiotics were effective, 25 fewer would intend to consult with the problem in the future, and 10 fewer would come back within the next year.

If you were an alternative therapist, or a drug salesman, you could turn those figures on their head and use them as a blueprint to drum up more trade: because we are all prone to see patterns where there is none, and more than that, to believing that our actions have results. This was demonstrated in a chilling experiment several decades ago. Subjects were recruited to play the role of a teacher trying to make a child arrive on time for school at 8.30am. They sat at a computer, on which it appeared that each day, for 15 consecutive days, a child would arrive at some time between 8.20 and 8.40.

Since this was a psychology experiment, the subjects were lied to: they did not know that the arrival times were entirely random, and predetermined before the experiment began.

Nevertheless, participants thoughtfully deployed punishments for lateness, and rewards for punctuality.

When they were asked at the end to rate their strategy, 70% concluded that reprimand was more effective than reward in producing punctuality from the child. It's a touching testament to their own beliefs about the world.

These people were convinced that their actions had an impact on the punctuality of the child, even though the arrival time was entirely random. The joy is, you have no way of knowing how many areas of your life this experiment might be relevant to. Now I'm going to dangle some goat entrails around my neck and get chanting.

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