June 20, 2007

don’t forget probability

In this video by Oxford mathematician Peter Donnelly, he poses the following hypothetical question:

Given an AIDS test which is 99% accurate, what is the probability you have AIDS if you tested positive.

The interesting part is this isn’t as easy as it sounds, and the rarity of the disease determines the answer as much as anything else. Let’s say for the sake of discussion that on average out of 1 million people, 100 have AIDS. We would then see the following:

  1. Of the 100 people who actually have AIDS, 99 people would correctly test positive. One person would have AIDS and the test wouldn’t catch it.
  2. Of the remaining 999,900 people who do not have AIDS, 9,999  would incorrectly test positive.

This means that of the 1 million people who get tested for AIDS, 10,098 of them would test positive, while only 99 actually have AIDS.

You can take a test which is 99% accurate, have it turn out positive, and still only have a 99/10,098 = 0.98% chance that you actually have AIDS.  An extremely accurate test says you have AIDS, and yet it’s extremely unlikely that you do.

This leads me to agree with former Prime Minister Benjamin Disraeli, who famously stated, “There are three kinds of lies: lies, damned lies, and statistics.”

June 6, 2007

orange power

A red-haired family claims to have been driven from their Newcastle home because of abuse. Why is the harassment of redheads dismissed as just harmless fun?

Here’s a joke. “What’s the difference between a terrorist and a redhead?”

Here’s the punchline. “You can negotiate with a terrorist.”
BBC News

Really? I knew the Irish and the British weren’t exactly best friends forever, but this seems bizarre. Also, there’s apparently an entire mythology surrounding redheads that I was unaware of. The first commenter writes:

Redheads are feared because they are believed in folklore to be the devil’s children and have red hair because they were conceived during their mother’s menstruation.A welsh proverb says “os bydd goch, fe fydd gythreulig” or “if he’s redhaired then he is of the devil”. Yesterday’s superstition has become today’s teasing.
L, Wales

My favorite though, is the BBC sidebar with relevant facts about redheads:

[There is] Disagreement over redheads’ reputed higher pain tolerance.

Oh, yeah, it’s why we have absolutely no objection to being beaten, it tickles.

June 2, 2007

how do you spell fucher?

It would not be incorrect to suggest that as a college student my investment strategies and budgeting could both be accurately qualifed with the adjective “non-existant”. College wasn’t real life, and this “future” people told me to worry about seemed intangible and distant at best.

But since I’m entering the phase of my life in which the next step is retirement, I figure it’s time to start looking at this elusive time period which exists beyond my next meal.

The following two short films I think anyone would find useful as they look at their financial future. Both films indirectly address lifestyle inflation, the concept that spending naturally increases to match your income unless you consciously try to avoid it.

Golly, those must be some expensive Sundays.

I guess I can spare $60/month

Powered by WordPress