Abuse of percentages

From an article at the New York Times, about the persistent racial gap in high school test scores:

Despite gains that both whites and minorities did make, the overall scores of America’s 17-year-old students, averaged across all groups, were the same as those of teenagers who took the test in the early 1970’s. This was due largely to a shift in demographics; there are now far more lower scoring minorities in relation to whites. In 1971, the proportion of white 17-year-olds who took the reading test was 87 percent, while minorities were 12 percent. Last year, whites had declined to 59 percent while minorities had increased to 40 percent.

I do not think that first percentage means what the journalist thinks it does...

Vaccine impact

It looks like the Andrew Wakefield, the doctor who, in 1998, kicked off the scare over the link between the MMR vaccine and autism faked his data. What effect has this had? In England, before the paper, 92% of kids were vaccinated. Now, it's "below 80%."

While 80% sounds pretty good, you need 95% immunization to be reliably free from measles outbreaks. There were 56 cases of measles in England and Wales in 1998, and 1,348 confirmed cases last year, with two deaths. It had been considered on the verge of elimination in 1994.

Germany had 614 cases in 2006, with two deaths. Those two children were ineligible to receive the vaccine for congenital immunulogical reasons. Such children depend on herd immunity for protection from the disease, as do children aged under 12 months, who normally are too young to receive the vaccine.

The US had 131 cases in 15 states (and DC) in the first half of 2008, with over 90% happening to unvaccinated children. That's the highest rate since 1996.

More economics graphs

Just a quick follow-up on my flurry of economic posts: USA Today has a well-done interactive set of three graphs, done by Moody's Economy, showing different aspects of their job-growth forcast, broken out by job sector:
(link found through FlowingData.)

Weekly percentages

I'm constantly looking for interesting example for my students that use percentages. I'm going to try to post a round-up of instances I've run in to at the end of each week.

• Tom Daschle is in political hot water right now for failing to pay about $128,000 in back taxes for unreported income in 2005, 2006, and 2007, mostly in the form of a car and driver that he was provided for free. (The amount does not include the interest he owes on the back taxes, which bring the total up to about $140,000.) Given that he's in the top 35% tax bracket, we can calculate the amount that the car and driver cost almost $366,000 dollars over those three years, or about $333 a day.
• A study (nicely described by the New York Times) had 10 and 11 year olds in a "virtual reality environment" decide when it would be safe to cross the street. They did it six times while talking on a cell phone, and six times not talking on the phone. (Half the kids used the phone first, the other half used it after the control crossings.) "[In] the simulation, talking on the phone increased the odds of being hit or almost hit by a virtual car from 8.5 to 12 percent, a 43 percent increase in risk."