A vindication of sorts. And goats.
There's a classic maths problem which I'm going to recount here, briefly, on the the basis that it may not be known to you all, despite the fact it will be utterly familiar to many of you - allow me a little latitude, please.
The situation is thus: You have been presented with three boxes. Inside one of the boxes is a fabulous prize (I'm not going to tell you what it is, but the knowledge that it is indeed fabulous should suffice) whereas the contents of the other two boxes can be safely assumed to be less fabulous. Naturally, you're terribly excited at the prospect of winning this (fabulous) prize, but you're somewhat vexed to find out that there are rules involved. Fortunately, the rules are rather simple: All you have to do is to choose a box. So you gaze down upon the three boxes before you and the knowledge that you have only have a one in three chance of winning starts gnawing at the very core of your being. You examine the boxes, but there are no clues to be had - all appear identical. Wracked by indecision, a single bead of sweat begins to trickle slowly down your forehead. You wipe it away listlessly. Which to choose you wonder. More moments pass. Soon you can stand the suspense no longer and fatefully point at the box nearest you. "This one," you announce to all, "I'll take this one." The wave of relief you feel at finally having made a decision doesn't last very long. "So you want that one," your mysterious opposite number (whom I haven't decided to imbue with any characteristics beyond a disembodied voiced - I'm in a lazy sort of a mood). "Are you certain? Are you sure? With so much riding on it, can you be certain you've made the right choice? Perhaps you might feel differently, were I to reveal... this!" And with that unseen gesture, the contents of one of the other boxes is laid bare before you, and you see, with perhaps a glimmer of relief, that it's contents are not fabulous. But your elusive companion is not yet done with his taunting. Having shown you the empty box, he now offers you your last choice. Keep what you have, or else change your mind and instead take the final box.
And this gist of the problem is this: Are you better off keeping what you have, or should you make that fateful final switch? Don't worry, I'm not about to launch into an explanation of the solution (although I can explain it well enough to convince myself), but I will tell you that the correct answer, as far as probability is concerned, is to make the switch.
Now what I really wanted to write about was the fact that this problem is generally known as the Monty Hall problem, after the eponymous host of an American game show from many years ago. However, I've always thought of it as the problem of Marilyn And Her Amazing Probability Defying Goats. Now see, the way you're now looking at me is the way people generally look at me, everytime I bring this up. You see, I had no idea why I thought of it like this. It's been the better part of a decade since I first came across this problem, and the details of that encounter have long been muddied in the mists of time. I could have been making it all up, admittedly, but somewhere out there I was convinced I would find an explanation that would account for Marilyn. And her goats.
And then today I discovered this. It seems that the problem was discussed in a newspaper column, written by Marilyn Vos Savant, and the framing of the question included... goats! It even stems from 1991, which is approximately the right time-frame.
And that's that really. All I have left to say on the subject is: Haha! See, I'm not mad!! I told you all, but you wouldn't believe me, would you! But I was right all along, wasn't I? Haha! Mad, they said! Haha. Mad, mad as a hatter. But who's laughing now? Hahaha! Hey, put that straightjacket down. Didn't you hear me? I'm sane, I said, sane! Oi, gerofff....
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okay, so dumbass here was looking for an article with a pretty goat border... I sped read the article.. missed all references to goats and was dumb struck.. or was that dumb struck before I read it..
Only using the apple F key did I locate the word goat, and felt all cheated... I didn't care about the boxes.. I cared about pretty goat pictures..
Should you be feeling particularly generous, please hunt down and email me pictures of goats to : M@thewbrown.com
Cheers!
I've always loved the Monty Hall problem. It's just counterintuitive enough to be utterly baffling.
I'm also a big fan of the birthday problem (i.e., if you have 30 people, there is a high (roughly 70%) chance that two will have the same birthday; if you have 50 people, the probability is about 97%). It makes for a great class demo...
I see you finally read 'The Curious Incident of the Dog in the Night-time', then ... I liked it a lot, but it was very sad.
Having had this problem 'splained in mathematical terms I must agree that, as Dr. Mija points out, counterintuitive and baffling are two words that describe it. Two more would be : "utter" and "piffle". To be fair, it's the application of the theoretical numbers to the actual situation that has always smacked of piffledom to me. It brings to mind some algebraic slight-of-hand a high school teacher once showed my class to prove that one could equal two, all supposedly within the rules of mathematics. Good thing I skipped out on calculus & trigonometry --probably would've made my head explode.
Ah, conditional probability. I've lost count of how many arguments I've fallen into based on the Monty Hall problem - it's one of those wonderful/horrible situations where a finely-honed dose of common sense does you absolutely no good whatsoever.
You're absolutely right - one should opt to switch choice. It's easily illustrated by drawing an outcome tree, but it's still counter-intuitive. Marvellous.
Hmm... that gives me an evil idea.
Hey, rAdam - what do you get if you differentiate cos(x^2)?
<spluff>
What you do know, it really did make his head explode. Don't try that at home kids, unless you have rAdam's to spare...
And Mija, speaking of birthdays, isn't a certain someone about due for another? Hmm..? :)
rAdam, I believe your algebra teacher should be had up on child abuse charges. However, the Monty Hall problem really does work as 'splained by the maths. If you set it up and actually do it, it does work out as the maths implies.
I know this, because the first time I came across it I was so confused I actually did. Although I couldn't afford a car, and didn't have any goats to hand, and had to use bits of paper turned upside down. I do not believe the presence or absence of ruminants affects the reliability of the results. Unless they wonder off, or eat the car.
Mind you, I am told that on the American TV show on which the scenario is based, the host used to cheat. Draw what conclusions you like about the relevance of probability theory.
I wonder whether the arguments that arise when people are first introduced to this problem have anything to do with a bit of psychology well known to economists: once someone takes possession of something, they tend to hold onto it, even when they clearly could benefit by trading. Interestingly people who participate in markets a lot - stock traders, footie card collectors, whoever - show this tendency to a much lesser extent. I wonder whether stamp collectors have a noticably greater tendency to believe the maths behing the Monty Hall problem.
Oh dear, I appear to be rambling ...