[prepend]

The key is in how you randomly select the sample from the population.

This was the author’s point. Just because you have 90k SO respondents doesn’t mean you can say anything about developers as a population. You can say lots of stuff about SO users. Or maybe developers who use SO. But just because you have lots of responses doesn’t mean you know what developers or jugglers or farmers or whatever population interests you.

The confusion rests with SO’s statement that their survey should be representative of developers in general (or CS graduates or whatever other than only SO visitors).

[balfirevic]

It's not even a random sample of SO visitors, as the there is, at the very least, self-selection bias.

[prepend]

I agree, although I think it’s more easy to correct for this bias to generalize to all of SO than to all programmers.