I've read just about everything Nate Silver has written since he was posting here as Poblano. Big fan. I read just about everything at the old 538 site and NYTimes version too.
But while everyone was watching the convention last night he posted something really dumb. Sometimes, especially when you write for a traditional outfit you feel the need to show how evenhanded you are. Here's the short version of his piece last night:
There's often a chance of rain in the summers of North Carolina and Colorado so why cancel the outdoor Obama speech in NC but not Denver 4 years ago?
Amazingly, what Nate wrote is dumb because of......arithmetic. And statistics. I know!
More below.
You see, when officials decided to move the NC speech indoors the Weather Channel, according to Nate, said there was a 30% chance of rain (upped to 40% a short while later).
So Nate did what Nate does, looked up some numbers:
Specifically, I looked at how often there had been rain or thunderstorms between 8 p.m. and 11 p.m. local time — the key hours for the speeches, and the logistics for getting everyone safely into the stadium.
In the Septembers since 2002, it has rained 13 percent of the time during these prime-time hours in Charlotte. Thunderstorms, however, are relatively rare during these hours, occurring just 3 percent of the time.
Nate assumes, and it was an assumption, that if there's a 30% chance of rain there was maybe a 15% chance of a thunderstorm.
But Nate, 15 is still a lot bigger than 3%, right? And even with just rain, I mean 30% is lot bigger than 13%. This is a weird argument, Nate. And why are you comparing a 30% chance of rain TOMORROW with a general chance of rain of 13%. GENERAL means nothing. Convention officials had a specific forecast and it was for the next day.
Anyway, Nate also says, "Why not cancel 4 years ago then?"
On August evenings between 6 p.m. and 9 p.m. locally — equivalent to 8 p.m. through 11 p.m. Eastern time — there is a thunderstorm 15 percent of the time in Denver, according to weather records between 2002 and 2011.
In other words, because Denver is such a thunderstorm-prone city during the summer, the general threat of a storm there was about as high as the specific threat of a storm in Charlotte on Thursday, based on the current forecast. If something in the neighborhood of a 15 percent chance of a thunderstorm were considered sufficient to force cancellation of an outdoor speech, Democrats ought never to have scheduled one in Denver to begin with.
WHAT? You have nothing in here about what the forecast for Obama's speech was the DAY BEFORE. So what if there's generally a 15% chance, what was the forecast the DAY BEFORE.
Further, you can do better than the Weather Channel for a local forecast. The best meteorologist in a local TV market (not any meteorologist, but the best) is going to do better. You really think convention officials didn't have a better guess than 30%.
But the way, it's raining in Charlotte.