NY wrote
Rod Speed wrote

Because you havent grasped that its an entirely statistical quirk.

and I don't see how the chance of Person A dying on any day is affected
in any way by how many other people happened to have been born on that
day (in one year or another).

It isnt, its entirely a statistical quirk.

Hmm. So for statistical reasons which don't have a cause (so I'm wasting
my time looking for one!), that fact that more people are born on one day
of the year than another means the each person is more likely to die on
the anniversary of when they were born than on any other date of the year?

Nope, the day they die is completely irrelevant. It’s the lumpiness in the
day of the year they were born on that produces the small statistical quirk.

That seems counter-intuitive because it is implying that the probability
of any one person dying on a given date (eg that person's birthdate) is
dependent on the number of (presumably independent *) events of other
people having been being born on that same date (though in a variety of
different years).

Certainly not a conclusion I could ever have reached no matter how long I
thought about it, but if you say so, I'll have to accept (but not believe)
it ;-)

You are still mangling the day you die in with the day you were born on.

The day you die on irrelevant to the statistical quirk.

I think the main problem is that the effect is based entirely on the
length of our calendar before dates start to repeat in new year.

Nope.

If the universe had been different and the earth had taken (for example)
400 days to go round the sun (so our dates repeated every 400 rather than
365 days), then there would still be a greater chance of someone dying 400
days (rather than 365 days) from their birth date.

ALL that matters is the lumpiness of the birth days.

It seems to ascribe some significance to one day (which relates to the
periodicity of the calendar) that makes it different from all others in
the year.

Nope.

(*) Maybe that's the problem: maybe they are *not* independent because the
distribution of births is based on climatic and social factors.

The different lumpiness with birth days and death days is irrelevant.