Letters from the November 6, 2004, issue of Science News

Another view

I suggest that world maps with countries colored by some statistical feature often would be more useful if done on a cartogram that is a compromise between population and size of countries, rather than on a map with a simple Mercator projection (“A Better Distorted View,” SN: 8/28/04, p. 136: A Better Distorted View). The problem of Earth’s curvature mentioned in the article would not seem to be an overwhelming obstacle. It is interesting that the electoral college presidential-voting system in the United States appears to amount to a rather good compromise between the relative importance of a region’s population, or number of voters, and its size.

Michael Haggerty
Burnaby, British Columbia

Take a risk

Your readers should be aware that the increased fatal cancer risk posed by annual whole-body CT scans, although still quite high, is in fact almost five times lower than that stated in “Scanning Risk: Whole-body CT exams may increase cancer” (SN: 9/4/04, p. 149: Scanning Risk: Whole-body CT exams may increase cancer), which says that annual scans from age 45 to 75 would increase a person’s lifetime risk of dying from cancer by 1.9 percent. By my calculation, current risk is 48 to 60 cancer deaths for every 240 people, so a 1.9 percent increase would mean an extra 0.9 to 1.1 deaths: 1 extra death per 240 people. While this increased risk is disturbingly high, it is 4.8 times lower than the risk quoted in the story, 1 extra death for every 50 people.

Todd P. Silverstein
Willamette University
Salem, Ore.

Study coauthor David J. Brenner of Columbia University says that the 1 extra death for every 50 people having full-body CT scans is correct. This would increase a person’s chance of dying from cancer from 23 percent to 25 percent. As presented in Science News, the 2 percent was ambiguous, he says, so it’s not surprising that Silverstein misinterpreted it as a relative risk factor, in which case the cancer mortality would have gone up only to 23.5 percent.—D. Parsell

Floored

It wasn’t the news of polluting runoff that caught my attention in “Paved Paradise?” (SN: 9/04/04, p. 152: Paved Paradise?), but the startling statistic that the 3 million annual increase in the U.S. population costs $480 billion in construction costs alone. That’s $160,000 dollars for each added person!

John Brooks
Lake Shastina, Calif.