0628: "Psychic"

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tulgeywood
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Re: "Psychic" Discussion

Postby tulgeywood » Wed Aug 26, 2009 6:05 am UTC

I recommend reading the book Psychological Subtleties by Banachek which is almost entirely on this subject. It contains most common responses to simple free choice questions (like think of a number between 10 and 50........... 37?) and under which circumstances they work best.

I used Mechanical Turk to do a survey on how best to phrase a question to influence what playing card a person picks when asked to think of one. If you ask the question (exactly as phrased) "Think of a playing card; first one that comes to mind. Not the Ace of Spades though as that is too obvious. First card that just feels right. Have it?" 34% of the time women will respond with Queen of Hearts (men it is around 12% and thus not as useful). The effect works based on how people respond to being told NOT to pick something. People on the whole default to believing they need to pick a card COMPLETELY different than the Ace of Spades. So even though you have explicitly only negated one choice, the Ace of Spades, they statistically (and by a wide margin) will no longer pick any Aces or any Spades. Spades normally make up 45% of all free card choices with no exclusions and Aces make up 46%. If you just exclude the Ace of Spades that changes to breakdown to 8% for Spades and 7% for Aces.

In summation 1/3 is much better than 1/100. Give it a try and keep in mind it is all in the presentation.

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Re: "Psychic" Discussion

Postby tulgeywood » Wed Aug 26, 2009 6:09 am UTC

Ace of Spades is chosen freely about 34% of the time. A lot of people look at it is being an obvious card though as it is the most notable (because it is designed in a different manner than any of the other cards).

Tass wrote:I do a bit of magic and mentalism. You can certainly get better than 1% odds on the miracle, but it is also a good thing to to have have a regular trick as back up. Or rather, when I want to do a trick, I often give it the chance of being a miracle first.

For example: pick out the ace of spades from a deck of cards and lay it face down on the table. Ask somebody to name a card. If they happen to say ace of spades ask them to turn the card over. There, free miracle. If they say something else, do the regular sleight of hand routine to make them think that the card on the table was actually the one they picked.

I usually use ace of spades because many people choose it, giving significantly better than 1:52 odds.

The good thing about the regular back up is that they will never know what you tried to pull, and therefor you can get another chance on the next trick.

lowlypeon
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Re: "Psychic" Discussion

Postby lowlypeon » Wed Aug 26, 2009 6:26 am UTC

But your odds slip a bit less than 1% if there are people who don't assume that "a number from one to one hundred" restricts you to integers.

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lentamentalisk
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Re: "Psychic" Discussion

Postby lentamentalisk » Wed Aug 26, 2009 6:48 am UTC

There is only one major hole in the theory of the comic, and it is something you guys missed entirely. I mean, you guys were not even remotely close...
If the person has seen Brothers Bloom, this trick will not work at all (read: this is straight out of the movie, only with numbers rather than cards.)
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Eternal Density
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Re: "Psychic" Discussion

Postby Eternal Density » Wed Aug 26, 2009 7:13 am UTC

I'm spannering blue celery and my number was 13. Then again I don't fit into the age bracket.

Fake psychic power is interesting when combined with game loss.
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Zorlin
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Re: "Psychic" Discussion

Postby Zorlin » Wed Aug 26, 2009 7:16 am UTC

Eternal Density wrote:when combined with game loss.

I just lost twenty dollars and my self respect.
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Eikinkloster
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Re: "Psychic" Discussion

Postby Eikinkloster » Wed Aug 26, 2009 7:23 am UTC

mrbaggins wrote:Try this one (works about 40-50% of the time). Say it out loud to friends. No idea if it will work in text form.

Think of a random two digit number... so, anything between 10 and 99.
Now, that's a lot of numbers, so let's narrow it down a little...
Make both digits odd. So like, 1, 3, 5 etc...
And because double digits are silly, make them both different.

So you've got a number now? Two digits, both odd, both different?

Spoiler:
37

(...)
Works best on children under 13 or so


Damn! The number worked on me. Is there any basis for that number?

As for 43 being 42+1... how is it surprising that xkcd readers would think of 42? Come on. Douglas Adams.

BTW, I am, indeed, psychic. It just doesn't perform at will, so I can't validate it and get James Randi's money.
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snowyowl
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Re: "Psychic" Discussion

Postby snowyowl » Wed Aug 26, 2009 7:31 am UTC

By the way: this is a comic about "romance, sarcasm, math, and language". The "math" part is this: by trying this you have a >1% chance (see previous discussions on how to increase your odds) of getting her in your pocket (whatever that may mean :P), and a <99% chance of just an embarrassing failure (which can still be salvaged if you then quip "Well, it only works about 1% of the time").

Mean outcome: (call it one night with her, depending on what you do next)/100 + 99*(minus 5 minutes of embarassement)/100 = 45200/100 - 99*300/100 = about 255 seconds. Yep, totally worth it.


Though not if you expect her to tease you about it for more than 7 minutes and 32 seconds.
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Eternal Density
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Re: "Psychic" Discussion

Postby Eternal Density » Wed Aug 26, 2009 7:34 am UTC

Zorlin wrote:
Eternal Density wrote:when combined with game loss.

I just lost twenty dollars and my self respect.
¡This cheese is ionizing my constituent atoms!
[edit]Wow, gotta love the filter.
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RThaiRThai
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Re: "Psychic" Discussion

Postby RThaiRThai » Wed Aug 26, 2009 7:49 am UTC

Well, I'm trying this, but I'm streamlining it.

I wrote this quickly to calibrate the probability I want:
http://dozydagger.com/more_misc/probability.html

I'm aiming for anything above 90%. I can do this more efficiently, though it will admittedly be less awesome, by sending an email to 20 people and telling them to choose one of the letters from my name.

This should be fun.

Pi is exactly three
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Re: "Psychic" Discussion

Postby Pi is exactly three » Wed Aug 26, 2009 7:50 am UTC

There's a variation which works 100% of the time but is easier for the mark to figure out how it's done. (And fails completely if they've seen the episode of Columbo which featured it...)

You: "Pick a number from 1 to 4."
Them: "1"
You: "Look under the phone."
They do, and there's a note with the message "I knew you were going to pick 1".

Of course, if they said 2 you would tell them to look under the lamp, if 3 then look under the blotter etc. By increasing the number of pre-prepared hiding places you could easily extend this to 10 choices, but it would get a bit unwieldy after that.

(Also enjoyed the Columbo episode where he exposed the psychic who had an ingenious method for faking his remote viewing.)
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pathtonoplace
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Re: "Psychic" Discussion

Postby pathtonoplace » Wed Aug 26, 2009 8:05 am UTC

I was recently trying to figure out what number 1-100 people choose most often. It was actually 42, and I have a guess as to why. I was also doing this test on omegle.com...which randomly connects you to a random stranger online. I think the results would be different if it was live in person. The freaky part, is the number I was saying was my number was 43...

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randomgeneral
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Re: "Psychic" Discussion

Postby randomgeneral » Wed Aug 26, 2009 8:29 am UTC

In the last few years I developed a habit of attempting to guess people's birthdays on first meeting them, just for exactly this kind of reason (and to make a quick quip if I got it wrong, as is usually the case). Now, I don't do it all that often, so the upper bound for the amount of times I've done this is 100 (easily, probably not even close).

However, in that time I've guessed it right - without any prior knowledge - THREE times. It's quite an amazing feeling, though you do come across slightly like a stalker :P

The thing is... I myself don't believe those odds. And I doubt there is any way you can 'tell' by looking at someone when they're born. So - statistical outlier, or latent psychic powers?! ;)

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Re: "Psychic" Discussion

Postby keithc » Wed Aug 26, 2009 8:50 am UTC

Eikinkloster wrote:BTW, I am, indeed, psychic. It just doesn't perform at will, so I can't validate it and get James Randi's money.

let me guess - it performs roughly in line with chance?

randomgeneral wrote:The thing is... I myself don't believe those odds. And I doubt there is any way you can 'tell' by looking at someone when they're born. So - statistical outlier, or latent psychic powers?! ;)

guess... Or analyze. You have been right about 3% of the time. On pure chance, you would expect to be right about 0.3% of the time. On such a small sample, a factor of ten isn't that unexpected. Add in the normal misremembering, people telling you that you are right when you aren't (surprisingly more common than the other way round), including off-by-ones, etc. and the number that you remember as being right is far higher than it really is.

frog42
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Re: "Psychic" Discussion

Postby frog42 » Wed Aug 26, 2009 8:52 am UTC

I actually am psychic.

When I say "I'm psychic", the majority response is "OK, what am I thinking right now?" The skeptic inevitably is thinking "I don't believe you, what am I thinking right now?" Telling them "Nothing except what you just said" will usually freak them out a bit.

Nobody ever bothers to think of what they want me to tell them they're thinking of.

Incidentally, despite being psychic, I have no idea what people are thinking, I just know from experience how the previous scenario works. What makes people think psychics have to be all-seeing, all-knowing? The gift of sight doesn't let me see beyond a certain low level of definition. The gift of hearing doesn't let me discern one voice in a crowded room. Being psychic is largely advanced pattern recognition. When your pattern recognition abilities significantly surpass that of others, congratulations, you're psychic. You won't be able to explain why you know certain things in advance, but you will know. It's no different than knowing that a red light turns green eventually instead of purple.

Also, stating your predictions often invalidates them (which is a huge relief when something really bad is coming). However, here's a pretty solid prediction: People will refute my claims. Others will ignore me all-together to negate my prediction. Reasonable folk will agree that it's possible to predict outcomes where you do not fully grasp the causes of those outcomes, giving the impression of psychic ability.

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Beaniedude
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Re: "Psychic" Discussion

Postby Beaniedude » Wed Aug 26, 2009 9:57 am UTC

I do this all the time but instead of them thinking of a number I always think of one.
A normal conversation follows:
Me: Ok, I'm thinking of a number. Any number. What is it?
Them: 53?
Me: No. 89? Yes! It was 89! I win!

Another variant is the Highest Number game.

Me: Wanna play the Highest number game?
Them: Ok...
Me: You go first.
Them: Err.... 549
Me: 550. I win!
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lunarul
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Re: "Psychic" Discussion

Postby lunarul » Wed Aug 26, 2009 10:46 am UTC

Tried asking 10 random strangers to pick a number between 1 and 100. Got these answers: 69, 1000, 30, 55, 4, 27, 25, 24, 7, 17
It's a very small sample, but I see 3 numbers ending in 7.
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topdownjimmy
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Re: "Psychic" Discussion

Postby topdownjimmy » Wed Aug 26, 2009 10:48 am UTC

http://www.washingtonpost.com/wp-dyn/co ... 04_pf.html


The reason is that humans are bad at making up numbers. Cognitive psychologists have found that study participants in lab experiments asked to write sequences of random digits will tend to select some digits more frequently than others.
...
We expect each digit (0, 1, 2, and so on) to appear at the end of 10 percent of the vote counts. But in Iran's provincial results, the digit 7 appears 17 percent of the time, and only 4 percent of the results end in the number 5.
...
Psychologists have also found that humans have trouble generating non-adjacent digits (such as 64 or 17, as opposed to 23) as frequently as one would expect in a sequence of random numbers.



I assume the "ending in five" thing is because numbers that end in five (and zero, I'm guessing) "feel" less random than numbers that don't. So already we can safely eliminate 20 numbers. And, what do you know, the digits in the number in this comic are adjacent.

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mrbaggins
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Re: "Psychic" Discussion

Postby mrbaggins » Wed Aug 26, 2009 10:59 am UTC

lunarul wrote:Tried asking 10 random strangers to pick a number between 1 and 100. Got these answers: 69, 1000, 30, 55, 4, 27, 25, 24, 7, 17
It's a very small sample, but I see 3 numbers ending in 7.


And either an idiot or a typo... (1000?)

Another good one...
"I'm so impressively intelligent (and slightly psychic). Want me to prove it?"
"Sure"
"I want you to think of a number. Any number. Minus 6, a billion and twelve, 76.9, doesn't matter. Got one? Now, what is it?"
"Uh.... <some number>?"
"Wrong!"

Thanks, Hitchhikers Guide!
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BillNormal
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Re: "Psychic" Discussion

Postby BillNormal » Wed Aug 26, 2009 11:45 am UTC

↓ tl;dr ↓
My first thought on this comic was that Randall made a mathematical error, then I went through the problem again. The first time I read the comic I saw the probability as 0.01%. I assumed you're also guessing a random number btw 1-100 which would be 1/100 x 1/100 = 0.01%. But the only reason I caught this is b/c in D&D the only time a Deity intervenes to save a devout character from permanent destruction is to roll two d100 and have them come up the same number. = very improbable
When you say 1% probability it assume you're saying the same number every time. And even then the certainty (or probability, if u will) of probability doesn't apply when dealing with small number of random samples. Probability only becomes standardized as you approach infinity. And then the sample of girls you pick isn't random at all, in fact it's highly bias (I doubt you go out with random women). Does that add another factor of randomness into the probability equation, does that reduce the random chance or picking a number based on social and personal taboos/superstitions etc.? Or is who you pick rendered moot by the fact the number is supposedly random in the first place.
↑ tl;dr ↑
Long story short: I thought you (Randall) had made a mathematical error! I was shocked and aghast! So much so I had to put everything else, I was doing, down (which was nothing) just to find a way to contact you and "fix" ur pic.

∴I would like to propose a question to Mr. Randall; Which is it? Are you guessing a random number each iteration or saying 43 every time?


BN

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a1s
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Re: "Psychic" Discussion

Postby a1s » Wed Aug 26, 2009 11:57 am UTC

This is "A webcomic of <...>math" ater all, so I think it's time to gather some statistical data.

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Re: BillNormal

Postby frog42 » Wed Aug 26, 2009 11:59 am UTC

Dear Bill,

Welcome to the wonderful world of the Gambler's Fallacy. Me choosing a random number every time and my friend choosing a random number every time has a 1% chance of us both choosing the same number on any given occasion.

This is the same as if I chose the same number every time and my acquaintance chose a random number every time.

Every iteration of the attempt is unique. The probability of two d100 coming up with the same number is 1/100. The probability of them coming up with a number someone else chooses is 1/100/100.

So, yes, you were wrong. Wrong wrong wrong wrong wrong. And I have surely made the exact same error in my time, as has everyone else. So suck it, us.

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Re: "Psychic" Discussion

Postby NO U » Wed Aug 26, 2009 12:01 pm UTC

BillNormal wrote:↓ tl;dr ↓
My first thought on this comic was that Randall made a mathematical error, then I went through the problem again. The first time I read the comic I saw the probability as 0.01%. I assumed you're also guessing a random number btw 1-100 which would be 1/100 x 1/100 = 0.01%. But the only reason I caught this is b/c in D&D the only time a Deity intervenes to save a devout character from permanent destruction is to roll two d100 and have them come up the same number. = very improbable


Very improbable indeed. In fact, a chance of 0.01, or 1%. Think with me here.
Rolling 2 d100s will give you 100x100=10000 possibilities. However, in 100 of those possibilities, the first d100 will match the second one (1 1, 2 2, ...., 99 99, 100 100). Thus we get a 100 out of 10000 chance of winning, and 100/10000 = 1/100 = 0.01 = 1%.

BillNormal wrote: When you say 1% probability it assume you're saying the same number every time. And even then the certainty (or probability, if u will) of probability doesn't apply when dealing with small number of random samples. Probability only becomes standardized as you approach infinity.


The probability, unfortunately, is the same whatever number he picks. Of course, the smaller the sample, the less likely it is the sample represents the actual probability, but that is another thing altogether

BillNormal wrote: And then the sample of girls you pick isn't random at all, in fact it's highly bias (I doubt you go out with random women). Does that add another factor of randomness into the probability equation, does that reduce the random chance or picking a number based on social and personal taboos/superstitions etc.? Or is who you pick rendered moot by the fact the number is supposedly random in the first place.
↑ tl;dr ↑
Long story short: I thought you (Randall) had made a mathematical error! I was shocked and aghast! So much so I had to put everything else, I was doing, down (which was nothing) just to find a way to contact you and "fix" ur pic.

∴I would like to propose a question to Mr. Randall; Which is it? Are you guessing a random number each iteration or saying 43 every time?


BN




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Just for that, you just lost a (the) game.

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Re: "Psychic" Discussion

Postby Lawman » Wed Aug 26, 2009 12:02 pm UTC

Strangely enough, recently I needed to write down a stream of two-digit numbers – not one straight after the other; there was a reasonable pause between me writing each down – and I certainly noticed that I tended towards certain numbers (although I neglected to keep hold of them). The problem with the "Human Random Numbers" thread is that the participants used tools or formulae for generating the numbers rather than simply going with instinct. I think that biased it a little.

I have some hypotheses on the numbers people tend to pick. I've listed their actual probabilities next to them. I would expect on average the the chance of a human picking these sorts of numbers would be higher than the figure I quoted.

  • Numbers that are or "look" prime (25/100)
  • Separate digits (82/91)
  • Containing the digits 3 or 7 (36/100)

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Re: "Psychic" Discussion

Postby thret » Wed Aug 26, 2009 12:03 pm UTC

We call cards all the time in poker. Daniel once called two consecutive perfect cards, I think it is probably the only time it has happened on tv:

http://www.metacafe.com/watch/820797/da ... ing_cards/

Sexy when it happens but of course nobody is stupid enough to think you are psychic.

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Re: "Psychic" Discussion

Postby a1s » Wed Aug 26, 2009 12:06 pm UTC

BillNormal wrote:1/100 x 1/100 = 0.01%. But the only reason I caught this is b/c in D&D the only time a Deity intervenes to save a devout character from permanent destruction is to roll two d100 and have them come up the same number. = very improbable

That's actually wrong. there are 100 numbers that can come up on that first die of yours (or that the Random Girl picks), so that makes for 100 cases that are valid (so it's 100 X 1/100 X 1/100= 1/100). since whatever Random Girl picks is a valid answer, you can simply think of the problem as happening after that pick and the number just being a constant you need to match (the probability is obviously 1/100).

ninja'd! at least 3 times, in fact :oops:

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Re: "Psychic" Discussion

Postby maja » Wed Aug 26, 2009 12:06 pm UTC

When you say 1% probability it assume you're saying the same number every time.

NO. No, no, no, no.
It doesn't matter wether you change it or not. the 1/100 applies to the probability of a match. if you want 1/100 x 1/100 then you need a third party picking a number and then the two of you both choosing the same one!!
Same thing applies to lottery tickets. Your chances of winning are not increased if you always play the same numbers as if "sooner or later their turn will come". Lottery draws are independent (the balls don't remember what they did last week). And the answers of the chicks you're trying to lay with this trick are also independent, so you can stick with 43 or you can alternate, the probability of getting it right doesn't change!

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Re: "Psychic" Discussion

Postby kevmus » Wed Aug 26, 2009 12:06 pm UTC

beat out by no u and others, but posted anyways for more explanation.
BillNormal wrote:↓ tl;dr ↓
My first thought on this comic was that Randall made a mathematical error, then I went through the problem again. The first time I read the comic I saw the probability as 0.01%. I assumed you're also guessing a random number btw 1-100 which would be 1/100 x 1/100 = 0.01%. But the only reason I caught this is b/c in D&D the only time a Deity intervenes to save a devout character from permanent destruction is to roll two d100 and have them come up the same number. = very improbable
When you say 1% probability it assume you're saying the same number every time. And even then the certainty (or probability, if u will) of probability doesn't apply when dealing with small number of random samples. Probability only becomes standardized as you approach infinity. And then the sample of girls you pick isn't random at all, in fact it's highly bias (I doubt you go out with random women). Does that add another factor of randomness into the probability equation, does that reduce the random chance or picking a number based on social and personal taboos/superstitions etc.? Or is who you pick rendered moot by the fact the number is supposedly random in the first place.
↑ tl;dr ↑
Long story short: I thought you (Randall) had made a mathematical error! I was shocked and aghast! So much so I had to put everything else, I was doing, down (which was nothing) just to find a way to contact you and "fix" ur pic.

∴I would like to propose a question to Mr. Randall; Which is it? Are you guessing a random number each iteration or saying 43 every time?


BN

p.s.
I just learned to do this today. I'm so happy ^_^

▲ ▲


Actually, the chances are the same either way. The DND example:
The first dice you throw will hit a random number from 1 - 100, right? But at this point, that number is useless. All it tells you is that the second has to be that number. The second has a 1/100 chance of doing that.

The long way (done with d6's because I'm lazy)

You have 2 dice. 1/6 each gives 1/36 of getting two sixes, right? (1/6 for the first dice, 1/6 for the second)
There's also 1/36 for getting two fives.
1/36 for getting two fours.

If you add them all up, you have 6/36, or 1/6.

See?

Whether the number randall picks is 43 each time or as random as a pseudorandom number generator can make it, the chances are the same if the person is actually being random. If they aren't (and humans usually aren't) then it's best to go with the highest probable answer.

heatsink
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Re: "Psychic" Discussion

Postby heatsink » Wed Aug 26, 2009 1:03 pm UTC

There's a website that apparently gathers statistical data on random numbers, http://www.arandomnumber.com/. It's been up for a few years.

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Agent Foxtrot
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Re: "Psychic" Discussion

Postby Agent Foxtrot » Wed Aug 26, 2009 1:11 pm UTC

I thought Randall's comics bit weak over the last couple of weeks, but today's was pure genius. Great. Simply great.

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Re: "Psychic" Discussion

Postby sora » Wed Aug 26, 2009 1:12 pm UTC

How about taking this a step further, like:

choose a number from one to ONE THOUSAND (just take it easy though)
Spoiler:
999?


Or, how about think of any word that first comes to your mind...
Spoiler:
sex...


think about your past
Spoiler:
you were six, and you have been molestered by a stranger; but you told no one about this incident; which you have held this secret for ages; dreaming of it over and over again every night while you try to sleep; but NO! How could you SLeEp?! After being RApeD by some JoHn dOE?! Oh, how did I know, I am simply a PSycHiC..that's all; I am NOt the OnE who MoleStered YoU, oh no...HAHAHhahahaaah


well, that's about the chance of a googleplex...or was it?~

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Re: "Psychic" Discussion

Postby Random832 » Wed Aug 26, 2009 1:18 pm UTC

lowlypeon wrote:But your odds slip a bit less than 1% if there are people who don't assume that "a number from one to one hundred" restricts you to integers.


You're not getting the simple elegance here - it's not the probability of his randomly chosen number matching the other person's, it's a (presumably empirically measured) probability of someone picking the number 43.

sora wrote:

Um, seriously uncool. @ everyone else, trigger warning on the third spoiler (at least until it gets probably erased by a mod)

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Re: "Psychic" Discussion

Postby Agent Foxtrot » Wed Aug 26, 2009 1:24 pm UTC

.cheeseofdoom. wrote:One problem, I know a lot of people with favorite numbers that aren't whole. My girlfriend's favorite number is 1000006.4.

Curious, why that number? Is it significant?

One of my favorites is called the "Dottie number", which is the irrational result of [imath]\cos{x}=x[/imath]. That is, if you take the cosine any number in radians, and keep applying cosine to the result, it will always eventually converge at 0.73908513321516064165531208767387..., though no one really knows why, since that number isn't significant anywhere else.

Interesting stuff.

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tzvibish
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Re: "Psychic" Discussion

Postby tzvibish » Wed Aug 26, 2009 1:38 pm UTC

Someone tell me if I'm wrong (I guess that goes without saying), but i have two problems with the math in this strip.

1) "1% of the time" does not mean each time he does the trick, he has a 1% chance. The way it's worded, it seems like he's saying no matter how many times he does the trick, only 1% of the attempts are successful. That would be pretty difficult to prove, and I would try and break out the calculus on this one, but this is a text-based forum post, so maybe someone else can help me on this one.

2) Let's assume he really meant that the trick has a 1% chance of success. The probability is actually a lot slimmer. We're assuming the number he's picking is constant. The truth is, both parties have to choose the same number. So the probability becomes 1/100 * 1/100. Or .01%. I guess the easy way out of this one is to say that it's a 1% chance for each party involved (perceived probability?)

I'm not a stats expert, so if I'm wrong, let me know.

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Invertin
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Re: "Psychic" Discussion

Postby Invertin » Wed Aug 26, 2009 1:39 pm UTC

I managed to pull this off to my incredibly predictable friend.

The number was Pi.

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Re: "Psychic" Discussion

Postby frog42 » Wed Aug 26, 2009 2:06 pm UTC

tzvibish wrote:Someone tell me if I'm wrong (I guess that goes without saying), but i have two problems with the math in this strip.

1) "1% of the time" does not mean each time he does the trick, he has a 1% chance. The way it's worded, it seems like he's saying no matter how many times he does the trick, only 1% of the attempts are successful. That would be pretty difficult to prove, and I would try and break out the calculus on this one, but this is a text-based forum post, so maybe someone else can help me on this one.

2) Let's assume he really meant that the trick has a 1% chance of success. The probability is actually a lot slimmer. We're assuming the number he's picking is constant. The truth is, both parties have to choose the same number. So the probability becomes 1/100 * 1/100. Or .01%. I guess the easy way out of this one is to say that it's a 1% chance for each party involved (perceived probability?)

I'm not a stats expert, so if I'm wrong, let me know.

http://ruleroftheinterwebs.blogspot.com
-featuring the xkcd comic strip!!


You're obfuscating the issue with worthless math (do I feel a laser sight pointed at me?). You are choosing from 100 numbers. One of those numbers is correct. You have a 1 in 100 chance of being correct. There are 100*100 possible outcomes, giving you .01% probability of a specific outcome, but 100 of those outcomes are positive.

My god science is dangerous when you believe it without first applying common sense.

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Re: "Psychic" Discussion

Postby Agent Foxtrot » Wed Aug 26, 2009 2:09 pm UTC

tzvibish wrote:Someone tell me if I'm wrong (I guess that goes without saying), but i have two problems with the math in this strip.

1) "1% of the time" does not mean each time he does the trick, he has a 1% chance. The way it's worded, it seems like he's saying no matter how many times he does the trick, only 1% of the attempts are successful. That would be pretty difficult to prove, and I would try and break out the calculus on this one, but this is a text-based forum post, so maybe someone else can help me on this one.

2) Let's assume he really meant that the trick has a 1% chance of success. The probability is actually a lot slimmer. We're assuming the number he's picking is constant. The truth is, both parties have to choose the same number. So the probability becomes 1/100 * 1/100. Or .01%. I guess the easy way out of this one is to say that it's a 1% chance for each party involved (perceived probability?)

I'm not a stats expert, so if I'm wrong, let me know.

http://ruleroftheinterwebs.blogspot.com
-featuring the xkcd comic strip!!

1) We have LaTeX. You can show any mathematical formula you want on these forums. For example, [math]\Gamma\left(z\right)={1\over{z}}\prod_{n=1}^\infty\frac{\left(1+\frac{1}{n}\right)^z}{1+\frac{z}{n}}[/math] :mrgreen:

2) You're assuming that he also randomly picks a different number each time. Sure, that further decreases his probability of success, but why wouldn't he just pick 43 every single time? Out of 100 girls, at least one of them is generally bound to pick 43 as well. Therefore, [imath]P=0.01[/imath].

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Sine Nomen
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Re: "Psychic" Discussion

Postby Sine Nomen » Wed Aug 26, 2009 2:14 pm UTC

this is why i never choose integers...

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a1s
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Re: "Psychic" Discussion

Postby a1s » Wed Aug 26, 2009 2:26 pm UTC

heatsink wrote:There's a website that apparently gathers statistical data on random numbers, http://www.arandomnumber.com/. It's been up for a few years.

Sadly he refuses to publish results...
tzvibish wrote:

but... 5 people explained it... in this topic... on this very page...

Code: Select all

a1s.faith.in_humanity --

frog42
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Re: "Psychic" Discussion

Postby frog42 » Wed Aug 26, 2009 2:26 pm UTC

Agent Foxtrot wrote:1) We have LaTeX. You can show any mathematical formula you want on these forums. For example, [math]\Gamma\left(z\right)={1\over{z}}\prod_{n=1}^\infty\frac{\left(1+\frac{1}{n}\right)^z}{1+\frac{z}{n}}[/math] :mrgreen:

2) You're assuming that he also randomly picks a different number each time. Sure, that further decreases his probability of success, but why wouldn't he just pick 43 every single time? Out of 100 girls, at least one of them is generally bound to pick 43 as well. Therefore, [imath]P=0.01[/imath].


Grr.... Despite your fancy math, you still FAIL. He can pick any random number he wants and the girl can pick any random number she wants. The probability will remain 1%!!!! EVERY TIME there are 100 numbers to choose from and ONE is right. Probability doesn't get much easier than this. 10,000 possible outcomes with 100 being positive. 100/10,000 = .01!!!!


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