Thursday, February 16, 2012

Post Script

Gutti, Gutti Macher, Whither Do Ye Wander?

Regarding the recent post on statistical illiteracy among people citing the Guttmacher Institute report on contraceptive use, a few clarifications are in order.

  1. The issue is not whether contraceptive use is a Good Thing, especially for Those People, that pregnancy is a disease, or that a baby is a tumor or parasite.  Female contraceptive use is certainly a good thing for guys, since it makes women sexually available without an implied responsibility for child-raising. 
  2. The issue is not whether lots of Catholic women use contraceptives.  Catholic doctrine is (mirabile dictu!) not predicated on current social popularity.  At one time, that would have meant approving of gladiatorial games.  After all, nearly everyone has at one time in their lives pilfered office supplies from their place of employment; yet, no one supposes either that the government should pay for burglary tools for kleptomaniacs ("property-challenged") or that the Church should be forced to pay for them despite teaching that stealing is wrong. 
  3. The issue IS whether the executive branch has the authority to issue decrees forcing anyone, let alone religious institutions, to pay for contraceptives.  If it is true that 98% use contraceptives -- and it isn't, really -- then they cannot really be hard to acquire.  One wonders how women got them for all these years since Griswold
Guttmacher did not even conduct a survey.  Instead they harvested data from another survey; viz., 2006–2008 National Survey of Family Growth (NSFG), conducted by HHS-CDC.  Just when pregnancy was reclassified as a "disease" is unknown.  Perhaps when babies were reclassified as "parasites" and "tumors."  All part and parcel of the Triumph of the Will, we suppose, and the general attitude that regards life with a sort of the-fun-is-over horror.  

Now, the NSFG applied only to women of childbearing age, taken as (15-44), and the percentages need to be understood as percentages of this cohort.  That lets a lot of nuns off the hook.  Let's take a look at the key Table 4 on page 21 of the report.  If the captured screen shot is illegible, the table can be found here:

The first thing we not is that 38% of the women in the cohort report that they do not use contraception.  If this is so, how can 98% of women use it?  Inquiring minds want to know.

Why % Means Nothing Unless You Know N
Easily said.  What Guttmacher did was take the percentages for contraceptive use and apply them only to the 62% who used contraceptives!  Thus, if 17.3% (of all women in child-bearing years) reported using the Pill, that became 17.3/61.8 = 28% (of all contraception users), and so on. 
It is also important to note that this means women who have used contraception at least once.  In table 15, we learn that something on the order of 30% of such women discontinued use for one reason or another.  Biggest reason for discontinuing the Pill was experiencing side effects.  For condoms, the biggest reason was that the boyfriend didn't like using one.  About 2% said their insurance did not cover it; and 3% said it was too expensive.  (These are percentages of Pill-users.)  Interestingly, about 10% of Pill-users stopped using the Pill because they got pregnant.
I found nothing in the NSFG relating to religion, so I cannot say how Guttmacher was able to reconstruct those particular percentiles.  Due to differences in methodologies, it is always tricky to combine the results of more than one study. 

Since Darwin came up somehow in the previous post, I thought I would ask Chuck what he thought of contraception:
Hence our natural rate of increase, though leading to many and obvious evils, must not be greatly diminished by any means. There should be open competition for all men; and the most able should not be prevented by laws or customs from succeeding best and rearing the largest number of offspring. (emph. added)
-- Charles Darwin, The Descent of Man, and Selection in Relation to Sex (2nd ed., 1882) pp. 618.


  1. Of course it makes sense that the original survey results were online; somehow I didn't even think to look. I suppose that's one of the dangers of statistics for the non-statistician -- already having some kind of numbers makes it hard to remember to go one step further.

  2. Thanks for the great analysis. We live in an innumerate society.

    Slightly off topic: it seems as if world population projections are going all AGW on us - for decades I've followed world population forecasts with amused interests. Ever since that fraud Ehrlich, we've had it beaten into our heads that we're doomed! DOOMED! by out of control population growth (which is why this is only slightly off-topic: world death-by-babies => we gotta stop babies! => birth control is sacred, and there is no more sacred duty than promoting it, at gunpoint if necessary).

    So, for decades, people both kept having fewer and fewer babies while stubbornly refusing to die in the inevitable global famines that never happened, while the world's population kept falling short of even the most 'optimistic' projections of the alarmists. Leaving aside the difficulties in what is, essentially, guessing how billions of individuals (many not even born yet) will chose to behave, for decades the trend line in these predictions has been dropping, until, about a decade or so ago, even the UN was admitting that world population would likely top out at about 8-9 billion in 2050 or so. And then start dropping, perhaps precipitously, like Japan. About 10 or 15 years ago, even the UN projections started to look like maybe we weren't doomed to crush each other to death, a la "the Mark of Gideon".

    Well, I started looking again at the UN reports, and it appears about 3-4 years ago, they changed their tune: now, it seems, we're once again DOOMED! The most likely scenario they predict is that, nope, there's no end in sight, we'll have 10B people by 2100! And then (blissfully unaware of the hubris of predicting how our great-great-grandchildren will behave) even MORE babies going forward! Quick, establish an extremely-well-funded supra-national executive to add contraceptives to the water supply! Or something.

    A basic concept that seem to get missed: population today is based largely on decisions made by individuals roughly from 80 years to 9 months ago. Another way to put it: Given current life expectancies, changes in total population numbers resulting from the decisions of individuals to have fewer children take about 80 years to show up. If everybody 80 years ago decided to have 2 children instead of 4, say, the population is still likely to more than double over the next 80 years before leveling off.

    So, as your little chart illustrating the 'success' of President Monroe's aggressive contraceptive policies (ha!) shows, population trends today are the result of decisions made long, long ago - when the trend leveled off in the US in the '60s, that was the result of decisions going way back to the 1920s, at least, and not of any policies or social norms just then taking hold in the 60's.

    Which means, ultimately, that we don't need to promote contraceptives, let alone supply them for 'free' with a gun to our head, even if we agree that the US population must stop growing - it's already stopped growing (net of immigration and the children of immigrants). For it to have stopped growing now, the social changes that lead to that stoppage would have to have started in about 1930, well before any mandate or even the wide availability of chemical contraceptives. As your chart shows, the trend goes way back before even then.

    This really requires an illustration, but, heck, this is com box...

    1. That is the best rejection of Malthusian logic I've ever seen.


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