[asdfaefasdf]

His writing indicates he believes his readers are "more intelligent", and he believes that first borns are "more intelligent". So yeah, if you were a second born, who was more intelligent, you'd dismiss his blog as BS, and would not be counted among the survey respondents.

[gjm11]

For that to work, you (our hypothetical more-intelligent second-born) would need to:

1. Have seen Scott express the opinion that first-born children are more intelligent.

2. Interpreted that claim in a way incompatible with your own experience of being an intelligent second-born (e.g., taken Scott to be saying first-borns are always more intelligent).

3. Been sufficiently offended (or otherwise unimpressed) by this to stop reading his blog when you would otherwise have been happy to read it.

For this to explain the apparent firstborn bias in Scott's survey respondents, thousands of potential readers would need to have done this. So, how plausible is it?

1. I've been reading Scott's blog for years and don't remember ever seeing him say anything like "first-born children are more intelligent" before this post we're discussing now. That doesn't mean he never did, and I'd be extremely unsurprised to find that he did -- but it does suggest that if he did it was easy to miss.

2. The distinction between "on average firstborns have an IQ one point or so higher than non-firstborns" and "firstborns are always smarter than not-firstborns" is not exactly subtle.

3. Well, anyone can get upset about anything, but this really doesn't seem to me like the sort of thing that would make thousands of people swear off an otherwise interesting blog in disgust.

I'm going to rate it very implausible. No way is anything remotely like this a non-negligible fraction of the explanation for the apparent firstborn bias in Scott's survey respondents.