Alternative explanation: this article is just not good science. It: * doesn't control whether the not-first-borns are outside the target demographic (too old o

Alternative explanation: this article is just not good science. It: * doesn't control whether the not-first-borns are outside the target demographic (too old or too young) * doesn't look at children without siblings * more importantly: is just a cross section, so no causal relationships can be gleaned from that * also highly problematic: is self-selecting, with no discussion of the distribution of people not participating. With a poll question like that that alone invalidates every result, as obviously it invites bias towards readers who deem themselves smarter than their siblings * is not discussing, and controlling for, alternative explanations for the observed result All in all the margin of error is almost certainly a multiple of the effect size, thus rendering the results useless. Which they are anyway, because you can only answer a question like the one given in the article with longitudinal studies.