Making tall or short of it
Candy Shedden, Boca Raton, Fla.
Including information about average height was considered, but after trying and failing to find a straightforward way to do it, we decided to leave it out. The “average height” for each study and each type of disease mentioned was different, since each study looked at distinct populations and used different methods. So, comparing your height with the average wouldn’t tell you much about your disease risk. But, to answer your question, the U.S. Centers for Disease Control and Prevention’s data from 1999–2002 show the average height for U.S. men as 5 feet, 9.3 inches and for women as 5 feet, 3.8 inches. — Solmaz Barazesh
Better controlling controls
Greg Skala, Nanaimo, Canada
The difference between average scores of the two groups of children on a written pretest that’s apparent in the graph was not statistically significant. The statistically significant difference between groups on control-of-variables knowledge emerged on a test administered shortly after each child received either explicit or exploratory instruction. — Bruce Bower
Intentionally or not, the article “Think like a scientist” clearly illustrated the problem of teaching scientific reasoning. The statement about the control-of-variables strategy, “Researchers hold constant all changeable features in an experiment except for one of interest,” does not make sense to a young person. While some engineers and medical researchers do single factor experiments, a single factor experiment is only marginally better than a no factor experiment. The issue is to model a process and, as noted in the article, the concept of modeling (using math and experiments) is critical for the understanding needed to make predictions.
David Sweetman, Dyer, Nev.
More astronomy cover coverage
David DeVorkin, Washington, D.C.
DeVorkin is the senior curator of astronomy and the space sciences at the Smithsonian Institution’s National Air and Space Museum.
Decades of close observation have convinced me not only that spiders and insects hold all the body-length per second records, but also that many event categories must be established to make sense of their athletic skills. A leafhopper, for instance, may spring several hundred times its own body length in one second. However, like a flea, it doesn’t spring toward a target, and it may land on its head as well as its feet. This is “dumb-jumping.” A jumping spider, on the other hand, knows where it’s going: A zebra jumper one-eighth an inch long can cover 2.5 feet per second in a series of five jumps and hit its target every time. Water skaters introduce a new venue for competition: surface tension. Ponderosa pine bark beetle grubs are the heavyweight bite-pressure champions. Parnid beetle grubs can hold on to a relatively heavier rock than can an abalone.
Why do the smaller creatures do better, and what are the limits of this advantage?
Karl Staubach, Benicia, Calif.
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