# bentarm comments on Amanda Knox: post mortem

• Over the summer, Eliezer suggested (approximately, I am repeating this from memory) the following method for making an important decision:

1. write down a list of all of the relevant facts on either side of the argument.

2. assign numerical weights to each of the facts, according to how much they point you in one direction or another.

3. burn the piece of paper on which you wrote down the facts, and go with your gut.

This was essentially the method I used in coming to my (probably slightly low) estimate of the probability that Knox and Sollecito were innocent. It just felt like they were innocent, and I saw essentially no reason to suspect they were guilty. I will note that the ‘pro-guilt’ site that komponisto linked to was just horribly devoid of anything that I might consider evidence (if anything, that site did more to convince me of Knox’s innocence than the pro-innocence site), and I did spend probably about 10 minute trying to find some evidence that they had missed, but completely failed.

On a different not, as I said at the time, 0.95 and 0.05 were just proxies for “pretty damn sure” and “pretty damned unlikely”—I have very little idea what 5% probability feels like, and I’m sure that if arbitrary scientific convention had settled on some different number for significance, I’d have picked that one instead. I have made some progress since a year ago on calibrating my estimates of small probabilities, but I absolutely do not think that I would be wrong approximately 1 time in 20 when making predictions to which I assign a probability of 0.95.

• This is a better summary of what I said than what I actually said, so I hereby declare your distorted version to be my true teaching.

• I have very little idea what 5% probability feels like

???

1d20!!!

• I don’t have an intuitive feeling for d20s, but it occurs to me that a useful resource might be a list of day to day events of certain probabilities so we can calibrate our intuitions to them.

Googling hasn’t found me anything useful, could anyone give an example of an normal event that has a 5% chance of occuring?

• You look at a clock and the seconds are :00, :01, or :02.

• It is a little over the chance that if you are dealt two cards from a standard deck of cards that one of them will be the ace of spaces. It is a little under the chance that if you are dealt three cards from a standard deck that one them will be the ace of spades.

It is roughly the chance that if you pick three random members of the US House of Representatives that at least two of the three will not be reelected.

If It is about half as likely as the chance that a given US soldier in Iraq over the last decade will have been killed or too badly injured to return to duty (generally estimated to be around 9%). ETA: This number is wildly off. Disregard.

It is slightly less likely than your expectation for Schrodinger’s cat to be alive if you run the experiment 5 times.

It is a bit under the chance that if you put your money on two numbers on a roulette wheel that one of them will turn up.

It is slightly over the chance that if you meet two random South Koreans that their last names will both be “Kim”.

ETA: Here’s a depressing one: It is around the chance that if you pick two children with childhood leukemia that they will both survive five years.

• It is about half as likely as a US soldier in Iraq over the last decade will be killed or too badly injured to return to duty (generally estimated to be around 9%).

Who exactly?

“One is always,” said Bertrand, “a shirker to some one else.”

“That’s true; no matter what you call yourself, you’ll always—always—find worse blackguards and better blackguards than yourself.”

“All those that never go up to the trenches, or those who never go into the first line, and even those who only go there now and then, they’re shirkers, if you like to call ’em so, and you’d see how many there are if they only gave stripes to the real fighters.”

“There are two hundred and fifty to each regiment of two battalions,” said Cocon.

“There are the orderlies, and a bit since there were even the servants of the adjutants.”—”The cooks and the under-cooks.”—”The sergeant-majors, and the quartermaster-sergeants, as often as not.”—”The mess corporals and the mess fatigues.”—”Some office-props and the guard of the colors.”—”The baggage-masters.” “The drivers, the laborers, and all the section, with all its non-coms., and even the sappers.”—”The cyclists.” “Not all of them.”—”Nearly all the Red Cross service.”—”Not the stretcher-bearers, of course; for they’ve not only got a devilish rotten job, but they live with the companies, and when attacks are on they charge with their stretchers; but the hospital attendants.”

“Nearly all parsons, especially at the rear. For, you know, parsons with knapsacks on, I haven’t seen a devil of a lot of ’em, have you?”

“Nor me either. In the papers, but not here.”

“There are some, it seems.”—”Ah!”

“Anyway, the common soldier’s taken something on in this war.”

“There are others that are in the open. We’re not the only ones.”

“We are!” said Tulacque, sharply; “we’re almost the only ones!”

He added, “You may say—I know well enough what you’ll tell me—that it was the motor lorries and the heavy artillery that brought it off at Verdun. It’s true, but they’ve got a soft job all the same by the side of us. We’re always in danger, against their once, and we’ve got the bullets and the bombs, too, that they haven’t. The heavy artillery reared rabbits near their dug-outs, and they’ve been making themselves omelettes for eighteen months. We are really in danger. Those that only get a bit of it, or only once, aren’t in it at all. Otherwise, everybody would be. The nursemaid strolling the streets of Paris would be, too, since there are the Taubes and the Zeppelins, as that pudding-head said that the pal was talking about just now.”

“In the first expedition to the Dardanelles, there was actually a chemist wounded by a shell. You don’t believe me, but it’s true all the same—an officer with green facings, wounded!”

“That’s chance, as I wrote to Mangouste, driver of a remount horse for the section, that got wounded—but it was done by a motor lorry.”

“That’s it, it’s like that. After all, a bomb can tumble down on a pavement, in Paris or in Bordeaux.”

“Oui, oui; so it’s too easy to say, ‘Don’t let’s make distinctions in danger!’ Wait a bit. Since the beginning, there are some of those others who’ve got killed by an unlucky chance; among us there are some that are still alive by a lucky chance. It isn’t the same thing, that, seeing that when you’re dead, it’s for a long time.”

--Le Feu (Under Fire), translation.

• Who exactly?

Oh. Hmm. I don’t remember where I saw this but that number is my background fact set. But when I look at the actual numbers this is clearly false. There have been around 30,000 people wounded or killed. (Source) and around a million who have served. That means that the probability of being wounded or killed at all is around .03, which is much smaller, and that’s even before the fact that I said wounded severely enough that one can’t keep fighting. Also in retrospect my number was obviously too high. Severe failure of rationality on my part. Ugh.

• I thought that number was highly suspicious, but I attributed it to the combined category (killed or too injured to return—which of course are very different things from the perspective of the individual concerned!).

• It’s somewhere between the chance of flipping 4 successive heads and the chance of flipping 5 successive heads with a fair coin.

• I was going to respond for I thought I knew many such things, but the few that did not involve rolling d20s involved rolling d%.

• I have made some progress since a year ago on calibrating my estimates of small probabilities, but I absolutely do not think that I would be wrong approximately 1 time in 20 when making predictions to which I assign a probability of 0.95.

My guess would be more that 1 in 20 wrong for a 95% confidence.