The only thing that puzzles me about this article (sent to me by Chris Wiggins) is that at first it’s presented as new: “The trend is buried deep in United States census data . . ” A couple paragraphs down, the article explains that these patterns were published last year by Lena Edlund and Doug Almond (who presented the results in our quantitative political science seminar). In any case, it’s an excellent news article and discusses the issues well. The only thing I’d like to see are some sample sizes, so that students who are given this article to read can compute the standard errors on their own.

Also, I have a couple problems with their graph. First, I’m not a fan of expressing sex ratios as #boys per 100 girls. To me, it’s clearer just to give %girls (or %boys) as a straight number: 48.8% or whatever. Second, it’s a mistake to make these as bar graphs starting at zero. Here, zero is not a reasonable baseline: it’s not like you’re really expecting to see zero girl births. I appreciate that they were trying to make a pretty graph, but in this case I’d go with a simple dot plot with +/- 1 standard error bars on the points. Or, better still, a line plot with time on the x-axis (one point for each decade) lines connecting the dots for each ethnic group, and also the vertical lines indicating standard errors.

Line plots are the best, and it’s great when you can put time on the x-axis.

Offspring sex probably also depends on environmental factors! Just something to keep in mind

http://www.sciencedaily.com/releases/2008/04/0804…