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Comment by aetherson | Hacker News Reader

It wasn't a default option (you were asked to enter into a text field your number of older brothers, older sisters, younger brothers, younger sisters).

He can't cross-reference by gender very well because his audience is overwhelmingly male, to the point where there's probably not a lot of statistical significance in the female audience.

But yes, I think that these data are very open to an "impossibly hungry judges" critique. If birth order effects were so very visible and so very strong, why haven't we noticed them before?

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>If birth order effects were so very visible and so very strong, why haven't we noticed them before?

I'm not sure where you're from but everyone I know (including a psychologist) sees birth order effects as very real with noticable effect. Have you never seen the stats of first borns being overrepresented in management, for example? Am I misunderstanding what you mean by "haven't noticed them before"?

Another example, having older brothers is one of the most consistent correlations with homosexuality for males. Birth order effects are absolutely visible.

As the article mentions in like the first couple of paragraphs, those results haven't generally withstood replication.

But more so, the effects in the Slate Star Codex survey are extremely strong. You'd expect that an effect that strong would be part of the common wisdom, not something that has to be teased out in a psychological study.

Well, to what you just mentioned, it -seems- to be a "common wisdom" that is disregarded by scientific study. So, maybe this is a case where the study was ill-designed, but everyone took it for granted?

I don't think it is common wisdom. Like, look: which of your coworkers are first-born? How many of them did you intuit that without explicitly asking?

That depends on the field. The guesses can be very accurate based on ancillary data like profession.

Anecdote time/thought experiment: and forgive me, I'm deliberately vague here.

Pretend there's a business somewhere.

Pretend they implemented a rule that said people had to enter a number/estimate into a box for a certain peice of information before they could proceed to the next box.

Pretend as an analyst you're looking at the values resulting some way down the pipe from that data entry point.

Do you think it reasonable to assume the distribution of numbers entered into that box that were invalid would be uniformally random?

If the answer is no, what numbers do you think people would enter disproportionately?

It seems tough to me to suggest that people are putting a default 0 in for older siblings but a default non-zero in for younger siblings. Why wouldn't they be consistent?

That said, I still don't believe these data. I don't know where the flaw is, but I none the less think there's a flaw. If it were a much smaller effect, it would be much more believable.

> If it were a much smaller effect, it would be much more believable.

Why do you think that?

We know that the SSC readership is in many ways quite distinct from the general population, so why do you find it surprising that it has correlations with birth order? Is it because you find it surprising that anything has correlations with birth order?

The effect would have to be smaller because most effects in psychology and sociology are pretty small. Else they would be obvious (common sense) even without field experiments.

I agree with the other comments here that it is a rather common sense effect, but it has eluded psychological research until now (which is what makes me question it). I know plenty of people who have a common sense view that birth order is important. So that part isn't missing. I can't even grasp how many times I've heard about the middle child being so different. Or being a typical little brother, etc.

For me the question is, if it is so obvious and measurable, why is this the first study that finds this obvious effect.

Most effects are small if you sample general population randomly. However, if you make a survey among basketball players, asking them for their height, you're going to find an extremely large effect. And in fact, birth order effect seem to be common wisdom too.

I like this way of approaching the problem, but I don't think it convincingly contradicts the GP's point; if participants were just entering invalid data to skip the question, then I think they would enter a similar type of number in both "# older siblings" and "# younger siblings", e.g. 0 and 0, or 100000 and 100000, or `rand(10)`.

The key observation is that I'd expect the same RNG to be used for each of the four fields.

I think you'd see much more `0`s in the fake data as well (it's a Schelling point). But if the fake-data population was disproportionately recorded as only children, that would have reduced the first-child effect, not attenuated it.

Was it optional though? He said some people didn't give him enough data, which makes me suspect first-borns were more likely to go "oooo this question is about me being awesome - better fill it in!" and other people to go "eh wtf I'll skip it".

All questions in the survey were optional. He had 2965 respondents for that question, out of 8077 total respondents, so that's a plausible source of bias.

> It wasn't a default option (you were asked to enter into a text field your number of older brothers, older sisters, younger brothers, younger sisters).

Is blank coerced into 0?

That would seem to explain the size of the effect.

No.

> why haven't we noticed them before?

LMGTFY

https://scholar.google.com/scholar?q=birth+order+effects

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