SciAm July, 1998 p.22 has a short article where they state that
the percentage of male births is slowly declining.
US: 1970 [51.3 %] 1990[51.2%]
Possible causes could be racial demographics, pollution, or frequency of
sex.
["...When couples have sex more often,
fertilization is more likely to occur early in the menstrual cycle,
which apparently increases the odds of male conception.
Some observers believe this conjecture explains why the percentage
of baby boys has usually increased after major wars."]
h Lau
hollywood hs
Bob Hayden wrote:
> ----- Forwarded message from Wolfgang Rolke -----
>
> >From [EMAIL PROTECTED] Sat Jan 22 10:47:51 2000
> From: Wolfgang Rolke <[EMAIL PROTECTED]>
>
> Hi,
>
> I am looking for information (journal article, web site ect.) on the
> difference in birth rates for boys and girls. Specifically I would like
> to find some real data and possible explanations for this phenomena. It
> seems to me that this would make a great example for an introductory
> stats course.
>
> ----- End of forwarded message from Wolfgang Rolke -----
>
> This should be on a FAQ list somewhere. Here are some bits and pieces
> selected not because they are great but because they are what I have
> at hand and answer some of the basic questions (while raising many
> more).
>
> >From _Populatiion: An Introduction_ by Johannes Overbeek, Harcourt
> Brace Jovanovich, 1982, pp.206-207.
>
> "Sex, of course, is one of the most readily observable components of
> population structure. People may misrepresent their age, but they are
> less likely to misstate their sex. The sex composition of a
> population is conventionally expressed by a summarizing device called
> the sex ratio, the masculinity ratio, or the ratio of males to
> females.
>
> "In the populations of most Western countries, including the United
> States, the sex ratio at birth is about 105%... For American blacks the
> sex ratio at birth is about 103%.
>
> "More male than female births is a feature of most mammals..."
>
> Then I have a preprint of a paper "Excess Female Mortality and the
> Balance of the Sexes in the Population: An Estimate of the Number of
> 'Missing Females'" by Ansley J. Coale at Princeton.
>
> "The masculinity ratio at birth has a limited range when calculated
> from large numbers of births with accurate registration. For
> aggregate births in 1962-1980 in 24 countries in Europe, the ratio
> ranged from 1.05 to 1.07."
>
> My recollection is that these differences are too large to be due to
> chance, but no one knows their cause, nor why more males than females
> are born. That pattern emerges in populaation records as far back as
> such records have been kept.
>
>
>
> _
> | | Robert W. Hayden
> | | Department of Mathematics
> / | Plymouth State College MSC#29
> | | Plymouth, New Hampshire 03264 USA
> | * | Rural Route 1, Box 10
> / | Ashland, NH 03217-9702
> | ) (603) 968-9914 (home)
> L_____/ [EMAIL PROTECTED]
> fax (603) 535-2943 (work)
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