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From: powers@noscvax.UUCP (William J. Powers)
Newsgroups: net.abortion
Subject: Re: Who's Life Anyway?
Message-ID: <1009@noscvax.UUCP>
Date: Sat, 13-Jul-85 15:55:10 EDT
Article-I.D.: noscvax.1009
Posted: Sat Jul 13 15:55:10 1985
Date-Received: Wed, 17-Jul-85 21:17:49 EDT
References: <556@bgsuvax.UUCP> <283@vaxwalislr.UUCP>
Organization: Naval Ocean Systems Center, San Diego
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> >> As I understand it (and what I was working from) the pill runs about
> >> 99.9% success.  Anyone want to look it up/correct me?
> >> 				Jean Marie Diaz
> >
> >    If this figure is correct, then a woman who is on the pill and who has
> >intercourse every other night has one chance in six of becoming pregnant
> >in any given year.
> >
> >Jeff Sonntag
> >
> 	A 99.9% reliability for the pill means that if a woman is
> using the pill and is sexually active, she has a .1% chance of getting
> pregnant in a given year, NOT each time she has sex.

This last statement is clearly wrong.  Though it is unclear exactly
what 99.9% reliability means, if the statement is to have any meaning,
it can't mean that a women has a 99.9% chance of getting pregnant in a
year.  First, let me say that such a statistic could certainly be
obtained.  You would just take data on how many people that use the
pill get pregnant in a year (note that this statistic is independent
of proper usage of the pill).  However, such a statistic is virtually
useless, since the result is independent of the number of times one
has sex.  If I have sex every night or once a year certainly makes a
difference in my chances of getting pregnant.  Such a statistic would
be useless in my being able to judge what my chances of getting
pregnant were unless I had some idea of the number of times this
average group of women had sex in a year.  If I had the answer to that
question, however, I could assign some estimate of the probabilty of
getting pregnant given that I have sex.  The point is that probability
of getting pregnant per sexual encounter while using the pill is a
useful statistic; the average number of pregnancies for women while
using the pill in a year is a useless statistic unless I know how many
times they had sex in that year.

Secondly, as I have pointed out previously, if a women has sex three
times a week, she will get pregnant on average of about once every 6.4
years.  That means that she has about a one in six chance of becoming
pregnant in any given year. (This result assumes that the chance of
getting pregnant while using the pill is 1/1000.)
However, it is worth pointing out that this probability undoubtedly
includes those cases where someone forgot to use the pill, and other
such misapplications of the pill.  It is also worth pointing out that
by simply abstaining during times that you think you're fertile (the
temperature method will give you a accurate way of doing this), then
the probability of getting pregnant while using the pill will decrease
dramatically.

It is interesting to note that in 1979 there were less than 3.9
million births.  If we use assume that one out of every four
pregnancies end in an abortion (the 1980 figure), then there were
about 5.2 million pregnancies in 1979.  In 1980 there were about 43.2
million women between the ages of 15 and 45.  These figures would
imply that the chances of getting pregnant in a year, even when you
want to, is about 1 in eight.  Either there are a lot of women who
cannot get pregnant or the number of sexual encounters is far lower
than three times per week.  I suspect that it is the latter assumption
which is greatly exaggerated.
Bill Powers