From: hrubin@skew.stat.purdue.edu
On 2014-12-18, Brett Smith wrote:
The arguments in the cited posting are based on a total misuse
of statistics. The various events are not independent.
Certainly using more methods of birth control will reduce the
chances of unplanned pregnancy, but may also reduce the chance
of a planned pregnancy succeeding. And the probabilities vary
from individual to individual. Your simplistic analysis is
plain nonsense.
> If you have sex, use at least 2 forms of birth control, or 3 if you have sex
> frequently. This means condoms and the pull-out method and/or the
> pill/hormonal or diaphragm/sponge. If you're a male you can only count on 2
> forms until you know your partner; condoms and pull-out. If you're female
> you can count on 2 or 3 forms until you know your partner; condoms and
> hormonal and/or diaphragm/sponge. Never rely on just the pull-out method or
> just the sponge, or actually just 1 form of birth control alone, period.
> 50% of all unplanned pregnancies occur in people using just 1 form of birth
> control and the other 50% used no birth control. Don't get pregnant unless
> you plan on it. Use 2 or 3 forms of birth control. All birth control
> should say on the package: use in conjunction with another form of birth
> control.
> Keep semen out of orifices for general protection against pregnancy and
> STD's.
> 2 or 3 forms of birth control is safer than a vasectomy or a tubal ligation.
> Proof:
> We're told that presuming an average of 80-100 sex act per year, the risk of
> pregnancy using the condom is 1 in 50 in perfect use, and 1 in 6 in typical
> use, and that the risk of pregnancy using hormonal birth control pills is a
> 1 in 333 in perfect use and 1 in 12 in typical use. This means at least 1
> in 333 couples using hormonal birth control in a given year will still get
> pregnant. That's not very good. Multiply that over 10 years, and it's even
> worse. To calculate the risk of using two forms of birth control, many
> people multiply 1 in 50 x 1 in 333 and assume a risk using both of 1 in
> 16,650 in perfect use and 1 in 72 (1/6x1/12) in typical use, which is still
> pretty bad. However, that is the yearly risk times the yearly risk. That
> is like if you took a single die, presumed a 1 in 6 risk of pregnancy with
> your birth control, thus the 1 side was pregnancy, the other five sides were
> not, rolled the die 2 times for a presumed 2 yearly acts, did that with
> another die/form of birth control, again, 2 chances for your 2 acts of sex
> on your 1 in 6 risk, so 2 in 6 = 1 in 3 risk on each die/form of birth
> control , and multiplied 1 in 3 times 1 in 3 calculating a combined 1 in 9
> yearly risk, when really it should be 2 in 36 which equals 1 in 18. Because
> rolling the 2 die together the risk of snake eyes is 1 in 36, roll them
> twice for 2 presumed yearly acts, the risk is 2 in 36. 1/6x1/6=1/36, x2 =
> 2/36=1/18.
> If the rates of pregnancy we're told are based on 100 presumed yearly sex
> acts, then the risk of using the condom per year in perfect use of 1 in 50
> must become a risk of 1 in 5,000 per _act_, and the risk per year in typical
> use of 1 in 6 must become 1 in 600 per _act_ . The risk of pregnancy of
> using hormonal birth control pills per year in perfect use of 1 in 333 must
> become a risk 1 in 33,300 per _act_, and the risk per year in typical use of
> 1 in 12 must become 1 in 1,200 per _act_. Therefore, I conclude multiplying
> 1 in 5,000 x 1 in 33,300 results in a 166,500,000 per act risk in perfect
> use and 720,000 per act risk in typical use, or presuming 100 sex acts, a 1
> in 1,665,000 yearly risk in perfect use and a 1 in 7,200 yearly risk in
> typical use. If you calculate this out to the number of people of our
> society it makes the risk of getting pregnant about equivalent to dying in a
> car accident, keeping in mind your individual risk must be in between
> perfect and typical use. If you could eliminate the risk of driving in a
> car you would, so use three forms of birth control when you have sex on a
> regular basis.
> If anyone wants to run this by several university statisticians and inform
> all high school sex-education teachers and planned parenthood, good.
> Because of the 5 million pregnancies per year, only 2.5 million of them - or
> half - are planned. Of the other 2.5 million unplanned pregnancies, 1
> million are terminated in abortion and 1.5 million are brought to term.
> Thus 1.5 million of the 4 million babies born per year are unplanned and 2.5
> million are planned. 37.5% of the nation is thus unplanned, due to a lack
> of a use of birth control, and this must surely have a negative effect upon
> the socio-economic status of our society. Remember half these unplanned
> pregnancies occur in people who use just one form of birth control.
> Send a memo to the Pope, too. Unsafe sex that takes a risk with another
> person's life - the baby's - is immoral. But sex that uses 2 or 3 forms of
> birth control is safe and moral, and birth control should thus be advocated!
> More research on safe sex at:
> https://groups.google.com/forum/#!search/safe$20sex$20guide/al
.california/rSqpVObXPkw/J9IXKiR9zu0J
> -----
> Permission to freely repost and reprint and use freely granted.
--
This address is for information only. I do not claim that these views
are those of the Statistics Department or of Purdue University.
Herman Rubin, Department of Statistics, Purdue University
hrubin@stat.purdue.edu Phone: (765)494-6054 FAX: (765)494-0558
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