I've grown a beard. Or, more accurately, I haven't shaved for a while, leaving the hair on my face to become more prevalent.
I quite like it. I haven't grown much facial hair before, except when being lazy for long periods without shaving, but until now it just formed facial mess, rather than a beard. Must be old age doing it.
A double-blind experiment is when, for instance, the pill given to a patient may contain the new experimental drug or instead just sugar, and the patient and the doctor giving out the pill don't know which it is. The doctor records that Patient X got the pill in box Y. The results over a large population are assessed. Some people just get better by themselves, and by using a placebo this effect is taken into account. If 15% of those on placebos get better, and 20% of those on the other pill, then it can be assumed that the pills effectiveness is 5% better than a placebo. If 1% on the placebo get better, but 40% on the real dose do, then that pill is a good one. If 2% on the placebo die during the trial of a heart attack, but 10% on the real dose do, that isn't a really good sign.
The doctor doesn't know which pill is which so that the doctor (consciously or not) doesn't influence the results either way.
Any experiment that tests for a result needs a control group (those on placebos, for instance) and results have to be compared to that control group to make sense. Otherwise, you get things like homeopathy or Reiki. Sure, some people are apparently healed, however how much of that is due to the placebo effect? How many would have been healed over time without it? How is it better than NOT doing it, or using something else?
Double-blind methodology made me think of a thought experiment.
You are God. You made everything, the universe, all the people. You want people to be good, and you will assess them after they finish with the first stage of their existence, that of 'mortal life' within the physical universe.
If you tell them what to do, you have directly influenced their behaviour. Are they being good, or doing good things, or treating each other well because you asked or told them to, or would they have been good anyway? If they did good out of fear or to personally gain, are they truly good?
If you don't tell them what to do, when it is time to assess them you can see them as they would have been. Those who have done good did it out of themselves alone. Are they good, then?
Due to popular (err.. one person) demand, I've added a pic. Sorry if it hurts :D