Tuesday, July 7, 2009

Psychic Abilities Test

I've created another toy, Psych Test.

The thing is fairly simple, you've seen it lots of times in movies. You have a standard 36 playing cards deck, and one by one you are trying to guess the next card suit color. Red or black.

Well... I'm not a psychic but I know what are you thinking.

"...50%...", right?

I bet, if you ask any of your friends or colleagues who is occupied in CS, mathematics or physics you'll have the same exact answer. But the thing is not actually that simple, and here is where the fun begins.

If you open up the link above and will click on the same exact prediction button during the whole test, the result will be exactly those 50%, well +/- 1% in some unlucky situations. You might repeat the test several times, it's pretty consistent almost without any deviations.

But if you will have the same test, but will actually try to guess the next card's color, you'll have a different result, usually in range between 40 and 60%. And you almost never will have 50% again.

You should try it to believe, you can check the source code too, there is no back door. Everything is fair.

So what do you think, how is that possible? Do you think it is you actual ability to predict the future affects the result?

I could tell a spooky story about underground CIA laboratories where they study those things since 60s, and that there is a standard measurement for such tests and an exact percentage which defines you as a proven psychic.

Or, if you prefer, we could think about the problem rationally. There are just four practically independent cases and two of them correct, so the result should be close to 50% every time, no matter which button you choose. But yet it's ain't like that.

As you understand this is not the test for a psychic abilities, this is a test for rational thinking.

Okay, I'm not going to marinade you any further, as you come here and read this far I owe you an answer.

The thing is simple but not that obvious. There's no mathematical or logical problem, every time you click any of those buttons, you've got an exact 50% probability to score. But in case when you click the same button all the time, you put your guess against an almost ideal random sequence generated by the computer. And that's why you have this pretty close 50% result every time.

But when you do the "guessing", your brain follows some patterns and tries to predict the next card. Yes, generally that's a random process and every guess as good as any other, but the distribution of those guesses in time is not such good as a random distribution generated by the computer. There are fluctuations and attempts to guess, which affect the quite short 36 cards selection and gives you the non 50% result.

The first time you test the computer's random numbers generator, the second time you test your own.

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