[R] Off topic --- underdispersed (pseudo) binomial data.

Rolf Turner r@turner @end|ng |rom @uck|@nd@@c@nz
Fri Mar 26 03:25:18 CET 2021

On Fri, 26 Mar 2021 13:41:00 +1300
Abby Spurdle <spurdle.a using gmail.com> wrote:

> I haven't checked this, but I guess that the number of students that
> *pass* a particular exam/subject, per semester would be like that.
> e.g.
> Let's say you have a course in maximum likelihood, that's taught once
> per year to 3rd year students, and a few postgrads.
> You could count the number of passes, each year.
> If you assume a near-constant probability of passing in each
> exam/semester: Then I would assume it would follow the distribution
> that you're requesting.


Thanks Abby.  I've experimented (simulated) a wee bit and found
that if I keep the numbers of students (undergrad and grad) exactly
constant, then the results are underdispersed.  However if the
numbers are allowed to vary then the results are overdispersed.

It seems that the universe is very reluctant to produce underdispersed
pseudo-binomial data!



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Department of Statistics
University of Auckland
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