Making tall or short of it

In your article “The genetic dimension of height and health” ( SN: 5/9/09, p. 22 ), some medical consequences of being either taller or shorter than the median height of the study group are explained. To help us all extrapolate these findings to our own lives, don’t you think it would have been helpful to state what the average heights for men and women are for the general population? 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

A graph provided with the article “Think like a scientist” ( SN: 6/20/09, p. 20 ) presents data about the understanding of control of variables by students from two different groups, those who received explicit instruction about the concept and those who were left to learn by an exploratory approach. However, the graph also appears to show that the students in the direct instruction group had a much higher mean score on prior knowledge of the concept. Especially for research about learning the concept of control of variables, I am surprised that better-matched test groups were not chosen for this research. 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.

When teaching people, trying to present information and methods that, on the surface, contradict observation will not be successful, unless one clearly notes how the experimental model is correlated to reality. And reality involves more than one variable and lots of interactions. I would suspect the results in the “discovery” versus “direct” instruction groups had more to do with the presentation and reasoning ability of the teacher than the characteristics of either method. My personal opinion is that some of both are required to engage natural curiosity. David Sweetman, Dyer, Nev.

More astronomy cover coverage

Readers of Science News are certainly a tough bunch — and evidently lovers of the perennial activity “what’s wrong with this picture?” The recent letters (“Astronomical art faux pas,” SN: 7/4/09, p. 30 ) taking umbrage at the “errors” on the May 23 cover might have noted, as was clear in the credits, that it is from a 1925 French publication for children, Le Petit Inventeur . Right or wrong is not the issue; the joy and romance of observing the heavens is — whether camper, wizard, meridian circle professional or, evidently, a French civil servant at the Paris Observatory. My only quibble is that the address label obscured the fourth quadrant. I’d love to know what lurks beneath. 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.

Speedy musings

Body-lengths per second as a measure of (relative) speed (as in “Hummingbird pulls Top Gun stunt,” SN: 7/4/09, p. 7 ) offers more entertainment than the incessant “miles per hour” reports about cheetahs, peregrine falcons, swordfish and such.

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.