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Scott P. Richert

Notes on the Guttmacher Institute's "Facts on Contraceptive Use in the United States"

By July 30, 2010

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As NFP Awareness Week 2010 draws to a close, I'd like to take a close look today at "Facts on Contraceptive Use in the United States," released in June 2010 by the Guttmacher Institute, the research arm of Planned Parenthood.

Incorrectly referred to by many news sources (not to mention commentators on the web) as a "study," "Facts" is really just a compilation of data on the use of various forms of family planning. As such, it relies on multiple studies performed by other organizations over different periods of time, which complicates efforts to get a clear sense of how the data contained therein correlates.

Still, "Facts" provides an interesting snapshot into the use of family planning, natural and artificial. Relying on a study published in Vital and Health Statistics in 2010, "Facts" notes 28 percent of U.S. women who practiced contraception between 2006 and 2008 used some form of the Pill, followed closely (at 27.1 percent) by tubal sterilization. The male condom comes in third at 16.1 percent, while all other forms of contraception rank below 10 percent. Near the bottom are "Periodic abstinence (calendar)" (most commonly known as "the rhythm method") at 0.9 percent, and "Periodic abstinence (natural family planning)" at 0.2 percent. (Oddly, the chart lists the number of calendar users at 300,000 and the number of NFP users at 100,000, which makes the percentages impossible, no matter what rounding method one uses. The same problems are found throughout the entire chart, however, which indicates that the actual numbers of users have been rounded up or down, not their percentage in the population. Thus, for calculation purposes, the percentages should be considered canonical.)

Much of the media coverage of "Facts" has focused on the table "First Year Contraceptive Failure Rates," which was compiled from four different sources. This table lists around 20 methods of contraception, along with "Perfect use" and "Typical use" failure rates. In a footnote to the table, the Guttmacher Institute notes that:

Most perfect-use rates have been clinically evaluated, but some are based on clinical expertise or “best guesses” (such as some forms of periodic abstinence, withdrawal and no method use).

However, the Guttmacher Institute provides no information on the methodology used to arrived at the "best guesses," nor does it note which forms of periodic abstinence are represented by "best guesses" rather than clinically evaluated rates.

In itself, that means that "First Year Contraceptive Failure Rates" is of limited utility compared with a clinical study such as the 2007 German study that found a 0.4 percent rate of pregnancy among couples practicing the symptothermal method of Natural Family Planning correctly.

But let's assume that the data on periodic abstinence listed in the table is a good-faith attempt to arrive at accurate numbers. In that case, here, according to the Guttmacher Institute, are the most effective forms of contraception, ranked by "Perfect use":

  1. One-month injectable and Implant (both at 0.05 percent)
  2. Vasectomy and IUD (Mirena) (both at 0.1 percent)
  3. The Pill, Three-month injectable, and the Patch (all at 0.3 percent)
  4. Tubal sterilization (at 0.5 percent)
  5. IUD (Copper-T) (0.6 percent)
  6. Periodic abstinence (Post-ovulation) (1.0 percent)
  7. Periodic abstinence (Symptothermal) and Male condom (both at 2.0 percent)
  8. Periodic abstinence (Ovulation method) (3.0 percent)

Every other method ranks below these, including Withdrawal (4.0), Female condom (5.0), Diaphragm (6.0), Periodic abstinence (calendar) (9.0), the Sponge (9.0-20.0, depending on whether the woman using it has had a child in the past), Cervical cap (9.0-26.0, with the same caveat as the Sponge), and Spermicides (18.0).

Many readers may be surprised to see three forms of periodic abstinence ranked so high, especially since news coverage of "Facts" painted a different picture. The problem is that the media focused on "Typical use" rates, and there, the table descends into near uselessness as a means of evaluating the effectiveness of Natural Family Planning.

Just as it did for "Perfect use" rates, the table provides separate numbers for "Typical use" rates for every form of contraception—except for the four forms of periodic abstinence, which it lumps together into a single "Typical use" rate. And that's where the problem begins.

"Periodic abstinence (calendar)" is not a form of Natural Family Planning; ovulation method, symptothermal, and post-ovulation are. The Guttmacher Institute acknowledges this in the first table ("Contraceptive Method Choice") by separating out "Periodic abstinence (calendar)" and "Periodic abstinence (natural family planning)." But when it comes time to discuss "First Year Contraceptive Failure Rates," the Guttmacher Institute tosses the calendar (rhythm method) of periodic abstinence in with the three forms of Natural Family Planning, and lists a "Typical use" failure rate of 25.3 percent for "Periodic abstinence."

Some might smell a rat here, but let's give the Guttmacher Institute the benefit of the doubt. Perhaps none of the three studies from which they gleaned their "Typical use" rates separated the rhythm method from Natural Family Planning. If that is true, however, the very least that the Guttmacher Institute should have done was provide a footnote explaining the lack of "Typical use" rates for each form of periodic abstinence.

Despite all of this, can we make our own "best guesses" at the "Typical use" failure rates for the three forms of Natural Family Planning (ovulation method, sympothermal, and post-ovulation), based on the data provided in "Facts"? Not really. "Facts" simply does not give us enough information. All we know is that 0.9 percent of women in the United States use the calendar (rhythm method) of periodic abstinence versus 0.2 percent who use Natural Family Planning.

In other words, almost 82 percent of the women lumped into the periodic abstinence "Typical use" failure rate of 25.3 percent are not using Natural Family Planning. According to the Guttmacher Institute's own numbers, in "Perfect use" the calendar (rhythm method) of periodic abstinence is anywhere from 3 to 9 times less reliable than any form of NFP. Therefore, it is reasonable to assume that calendar (rhythm method) users are responsible for the bulk of the periodic abstinence "Typical use" failure rate. (Perhaps disproportionately responsible, too, since the rhythm method cannot properly account for even minor variations in a woman's cycle, whereas all forms of Natural Family Planning can.)

Because "Facts" does not provide enough information, readers need to look elsewhere for reliable typical-use data. The various organizations listed on the Natural Family Planning Resources page keep track of such studies and update their websites frequently with the latest information. Their numbers, usually stated as success (rather than failure) rates, generally range from 95-98 percent in "Typical use," and over 99 percent in "Perfect use."

One final thing to note about "Facts": The "Typical use" failure rates listed for most forms of artificial contraception are much higher than most people realize. For instance, the Pill is listed at 8.7 percent; Diaphragm, 16.0; Sponge and Cervical cap, 16.0-32.0; Male condom, 17.4; Female condom, 27.0; and Spermicides, 29.0.

Why don't we normally hear such high numbers from the advocates of artificial contraception? Because, when arguing against Natural Family Planning, they generally attack proponents of NFP for providing perfect-use failure rates, while they themselves provide perfect-use, not typical-use, failure rates for artificial contraception. But if "Facts on Contraceptive Use in the United States" is to be trusted, when we compare apples to apples—"Perfect use" to "Perfect use"—the range of failure rates between the most commonly used forms of artificial contraception and Natural Family Planning is very small.

- - -

UPDATE: A reader points out that there is one way to arrive at a rough breakdown of "Typical use" failure rates for the three forms of NFP and the calendar (rhythm) method. Based on the fact, according to the Guttmacher Institute, that almost 82 percent of women using periodic abstinence are using the calendar (rhythm) method rather than one of the three forms of NFP, we can calculate an aggregate "Perfect use" failure rate for all forms of periodic abstinence. Since "Facts" doesn't give a breakdown of how many women use each form of NFP, we have to assume equal distribution. After that, the calculation is simple:

  • 0.82 x 9 (the "Perfect use" for Calendar) = 7.38
  • 0.06 x 3 (for Ovulation) = 0.18
  • 0.06 x 2 (for Symptothermal) = 0.12
  • 0.06 x 1 (for Post-ovulation) = 0.06

Thus the aggregate "Perfect Use" rate for all four forms of periodic abstinence, assuming even distribution of the three forms of NFP, is 7.74 (7.38 + 0.18 + 0.12 + 0.06).

With that in hand, we can calculate the correlation between the aggregated "Typical use" rate and the aggregated "Perfect use" rate:

  • 25.3 / 7.74 = 3.27

And then we can take that multiplier and apply it to each of the "Perfect use" rates to determine a rough "Typical use" rate:

  • Periodic abstinence (calendar): 9 x 3.27 = 29.43
  • Periodic abstinence (ovulation method): 3 x 3.27 = 9.81
  • Periodic abstinence (symptothermal): 2 x 3.27 = 6.54
  • Periodic abstinence (post-ovulation): 1 x 3.27 = 3.27

Please note that a) these are rough numbers, because, as noted above, "Facts" doesn't give an actual distribution of the users of the three forms of NFP; and b) the multiplier most likely is low for calendar (rhythm) users, because the calendar (rhythm) method cannot account for variations in a woman's cycle and therefore is considerably less accurate in "Typical use" than the three forms of NFP; which means that c) the multiplier is most likely high for the three forms of NFP.

All that said, perhaps we can now see why the Guttmacher Institute didn't make "best guesses" on the "Typical use" failure rates for the three forms of NFP, even though they were willing to make "best guesses" on the "Perfect use" rates. Simply compare the rates to the Guttmacher Institute's own listed "Typical use" failure rates for the most commonly used forms of artificial contraception:

  1. Periodic abstinence (post-ovulation): 3.27
  2. Periodic abstinence (symptothermal): 6.54
  3. The Pill: 8.7
  4. Periodic abstinence (ovulation method): 9.81
  5. Male condom: 17.4

While these "Typical use" failure rates for the three forms of NFP are a little on the high side compared with clinical studies of actual NFP users, they compare quite favorably to the Guttmacher Institute's "Typical use" failure rates for the Pill and the male condom.

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