Wednesday, February 22, 2006

And the rain it raineth 32.65% every day

What's with all these 'chance of precipitation' percentages you get in weather forecasts nowadays? Remember the good old days when the day was going to be either 'sunny' or have a 'chance of rain' or 'light showers' ? So much more evocative than saying 20% or 30% or 40%. I mean, back then you could stand in your window with your jaw tightly clenched and watch the rain pouring down and take pride in the fact that you were living through an honest to god 'Thunderstorm' - no, really, look, it said so in the paper. Now you're just another in an endless series of statistics - just some poor, lonely 80% stuck inside your apartment.

I mean to begin with, what are these numbers supposed to mean anyway? Is 30% probability high? Is 40%? Look, I'm as good with numbers as the next guy, but do you really think I want to spend precious minutes of my day trying to weigh the actuarial pros and cons of carrying an umbrella?I mean okay, so if I were trying to forecast the yield of rice in Western Punjab or something, I could see how % chance of precipitation would be useful, but I just want to know if there's a chance I could get wet, for crying out loud. What do I need the stupid weather forecast for if I'm going to have make up my own mind anyway? It's the certainty one read weather forecasts for, the blithe arrogance of voice that proclaimed that the day would be sunny, and brooked no dissent. Never mind if it actually turned out to be the rainiest day of the year, and you got caught in a downpour and your favourite coat turned into the pelt of a mangy hyena - at least you had someone else to blame. "But the newspaper said it was going to be sunny", you could plainitively bleat, and the day's scapegoat would be duly slaughtered by those around you.

Now, of course, the decision's left up to you. Oh, you can still claim that the weather forecast gave you misleading information, but that's like saying you thought there were WMD's in Iraq - the responsibility's still yours. This means you have to agonise over it. All those old phrases about pessimists and optimists and glasses full and empty come back to haunt you. Is a 10% probability of rain reason to carry an umbrella? Am I just being paranoid? Maybe I'm obsessive compulsive. Maybe I'm going to end up like Jack Nicholson in that movie. Or worse, like Jack Nicholson in that other movie. Or like Jack Nicholson in that third one. Or like Jack Nicholson in real life! Help!. See - all that trauma just because some snivelling Princeton graduate of a copy editor decided to save 6 characters of type in the weather column. Was it worth it, I ask you?

The worst part about these percentages is the sense of hope they give you. I mean in the old days it would just say 'Rain' and that was it. You would stay home. You would make yourself some cocoa. You would bring out the little solitaire table and your deck of cards. When the sunshine came beaming through your window you would smile and shake your head. You weren't going to fall into that trap, no sirree, you'd read your weather forecast - they weren't going to get you that easy. When the whole day passed and it didn't rain at all, you'd tell yourself you were being prudent. Why take a risk with your health? Better to save it for a rainy day. Or whatever.

Now, though, it says 80%. Which means (you do the math at your usual lightening speed) that there's a 20% chance that it won't rain. You decide to think positively for a change. You look scornfully at people wandering about with umbrellas - why is everyone so pessimistic these days, you think to yourself. After you've finished changing out of your damp clothes you brood over the injustice of it all. It could have stayed clear and it didn't. This is no longer just about the weather - it's about your personal bad luck. Things never work out for you, do they? You must have done something to deserve it. You feel vaguely guilty for not making that 20% chance come true.

People who like these percentages will argue that it gives you more information. Fair enough. Let's say you really want to build a full-blown economic model to help you decide whether you should wear that raincoat / carry that umbrella. Would just telling you the probability that it will rain be enough? What about the probability that there'll be a gusting wind and the rain will be coming at you horizontally and you'll end up getting drenched anyway? What about the probability that your cheap import of an umbrella will choose the one moment when the rain is pouring down heaviest to get blown away or bent out of shape? What about the probability, that you'll step out of your door and stand there for the next five minutes cursing your umbrella because it won't open. What about the probability that the person you're having dinner with will not bother to bring her raincoat and so you'll have to do the chivalrous thing and give her yours (MR are you listening?)? What about the probability that just as you're getting to office all dry under your umbrella and congratulating yourself on having read and correctly interpreted the 60% chance of rain, some speed demon of a bus will go through a puddle and drench you through and through? If you really want me to figure out whether it's worth carrying an umbrella or not, how about giving me some of the facts I really need, instead of this one piffling number?

The one good thing about these % things (I have to admit) is that they give you hourly forecasts, so you can really plan your life. What you want to go for dinner NOW? Are you kidding me? Didn't you see that the chance of rain just quadrupled from 5% to 20% two minutes ago? I'm not going out in that!



dazedandconfused said...

Hi Falstaff
Saw ur comment at youthcurry and followed the trail to here. Loved some of your posts, the gay Bhishm and the romantic-gestures-going-wrong one. Nice.

Neela said...

WHAT?!! You mean you don't actually DO the Expected Utility Thing? In your head?? Falstaff, YOU, you, who wrote incomprehensible posts equating romance to game theory and drew the most beautifully meaningless graphs on arranged marriages and the normal distribution, you now break it none too gently that you are a normal human being who doens't like probability?? What next - will you actually get taken in by those Linda is a bank teller thingies we all laugh at? Noooooo! Please let something in this world remain eternally insane and totally pathological.

Yours, in deep grief


Anonymous said...

lol@Neela :D

The ramblings of a shoe fiend said...

Please don't hate me. You have been tagged.

Falstaff said...

Andy: Thanks. Welcome to the blog.

Neela: Expected Utility Things? No, no, leave that sort of stuff to the economists. Though, come to think of it, you're not referring by any chance to the multinomial logit I run with covariates like necessity of going to class, time since I bragged to someone how gorgeous the weather in Philadelphia was, length of small intestine of the day's squirrel sacrifice etc, are you? See that kind of stuff is just basic intuition - from a Weather Report you expect fact-based analysis

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