

Are 80% of Harvard Students First Borns? - lwc123
http://larrycheng.com/2010/03/06/why-are-80-of-harvard-students-first-borns/

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reader5000
Eh, thats not very good evidence of the claim, and wouldn't over 50% be first
born anyway? I dont know the average distribution of child-sizes but I would
assume almost half of people in the US are first borns (including only-
children).

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swwu
The "average number of own children under 18 per family" for "familes with own
children under 18" was 1.86 in 2009 (and has been within 0.1 of that since
1978), which means about 1/1.86=~54% of all children are first-borns...

I don't think we have enough information here to actually verify but I suspect
80% vs 54% is still a statistically significant difference.

But it's pretty obvious that the 80% number is an arbitrary guess, so I'm not
sure exactly where I stand here.

source: <http://www.census.gov/population/socdemo/hh-fam/fm3.csv>

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tel
No, it depends on the distribution. Let's say (as a first guess) that number
of children follow a poisson distribution. A poisson distribution with mean of
1.84 has 74% of children being first borns.

There are a lot of reasons why a poisson model probably isn't great, but it's
worth pointing out that a model with more density near zero is probably likely
and implies that first borns are more popular than the they look.

74% versus 80% isn't anything to write home about.

Moreover, as Mz points out, only-children are a totally different case.

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sasmith
A Poisson distribution with a mean of 1.84 results in about 45% of children
being first born. In fact, the best you can do with any distribution is 54%.
For example, if there are 10k couples, then there will be 18.4k children born,
at most 10k of which can be first born; and 10/18.4 = 54%.

In fact, the only thing that matters for the distribution (once you know the
mean) is the number of childless families, since they could have had a first
born but didn't.

I haven't been able to figure out where 74% comes from. Is there some way to
sample on a per-family basis to come up with this?

edit: spelling

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tel
More like a fundamentally stupid mistake of inverting my parameters when I
checked the number, getting a result in tune with the article, and then not
thinking it through at all. It'd be possible to have a whole great deal of
families with 0.1st children, but that's just the egg on my face.

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shalmanese
Inferring temperament from birth order is largely pseudoscience. Wikipedia has
a good summary: <http://en.wikipedia.org/wiki/Birth_order>

"Birth order is defined as a person's rank by age among his or her siblings.
Birth order is often believed to have a profound and lasting effect on
psychological development. This assertion has been repeatedly challenged by
researchers, yet birth order continues to have a strong presence in pop
psychology and popular culture."

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vomjom
There are many obvious problems with this argument:

1\. The 80% number seems to be pulled out of the air. It could be a counting
error or a statistical aberration of that class, and the real Harvard number
could revert to the mean.

2\. The type of parents who could send a child to Harvard is a biased sample
of the general population. It will mostly tend towards rich, white (or asian)
families, who generally will have less children.

There's definitely not enough information to infer that first-borns are any
different.

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antidaily
Or maybe if they're not rich, they can't afford to send child #2 there.

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ascuttlefish
I figured it was because the second and third born were too busy working their
butts off in the military and the clergy to have time to spare.

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RiderOfGiraffes
Interesting that although I am the second of two, the "Only Child" description
matches me much, much more accurately than the others.

It's always the way that statistics are fine in aggregate, but for the
exception, it's 100%. For me, the descriptions of the characteristics of the
"child-by-place" are simply all wrong.

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Mz
I hesitate to say it, but maybe a lot of them are 'only' children and it
relates (at least in part) to parental ability to afford Harvard? Just like
big cities in America tend to have fewer kids because they are expensive to
live in, so families move someplace they can afford to raise their kids.

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whyenot
This was my first thought as well, but my understanding is that if you are
accepted at Harvard they will provide financial aid for 100% of need, which
means parents pay what they can afford -- it can actually be cheaper to go to
Harvard than a state school that doesn't have the funds to meet 100% need.

Maybe single children have better academic preparation? Should be easy to look
at that.

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jackowayed
Need is a hazy thing. They will meet all of what they define as your need, but
what you "can pay" often means a substantial sacrifice when it comes to
standard of living. This is especially bad if your parents have been paying
what they "can pay" for the last 4 years for an older sibling.

Also, it's gotten a lot better in the last few years, which is after he moved
through Harvard.

About 3(?) years ago, they, along with a few other upper-echelon colleges (I
know Stanford did) moved to a much more liberal definition of need and totally
got rid of loans from financial aid programs. Now, theoretically, if your
family makes <$60k, you pay nothing, and <$100k you pay no _tuition_ , but pay
room & board and such. There's more variables than just family income, and you
always have to add to the "nothing" or the "no tuition" a reasonable figure
for the student to make from having a part-time job during the year and full-
time over the summer, but it's still substantially more generous than it was.

It would be interesting to see if those policies changed the percentage that
are only children.

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jessriedel
That's quite a liberal definition of "need".

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jackowayed
Yes, it is. It used to be substantially worse, though, and other than a few
top colleges, it still is.

Example of the difference: my "estimated family contribution" according to the
FAFSA is about $10k more than what Stanford estimates they'll make me pay
(though I haven't seen the final number, yet).

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enthalpyx
These descriptions reminded me of horoscopes... I saw characteristics of
myself in each one.

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Confusion
Yeah, that's the Forer Effect[1] at work.

[1] <http://en.wikipedia.org/wiki/Forer_effect>

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fadmmatt
Back when I took calculus in high school, the instructor asked for a show of
hands for first-borns. All hands but one went up--well above 80%. I've
wondered why that was so ever since. Why weren't middle and younger children
pushing themselves to get into the "advanced" math classes?

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fierarul
Because parents put much more pressure on the first born.

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greenlblue
Epic fail. All his descriptions do not even remotely describe me and my
brother.

