Fact or Fiction? Understanding Statistics
Statistics have the flavor of hard fact. However, the key to judging their real value lies in understanding the vast underpinnings of a simple statement like “Ninety-eight percent of Catholic women use contraception.” Especially when that statement is used as ammo in a high-octane debate on religious freedom.
Statistics never come out of the blue. They are notoriously prone to manipulation, because they are always an interpretation of available data. Understanding how that data was compiled and who interpreted it are key to deciding what effect any given statistic should have on our opinions and decisions.
Statistics work based on the principle that the sample surveyed, or data set, will always represent the whole population.
In this case, the affirmation that 98% of Catholic women use contraception is based on an April 2011 study by the Guttmacher Institute (study here and additional data here). The study of 7356 women ages 15-44 analyzed religious-affiliation, sexual activity and use of contraception.
While 7356 women is a good-sized sample, only 1839 (25%) of those women self-identified as Catholic on the survey. Based on weekly mass attendance, only 30% of those who said they are Catholic are practicing. That brings the sample down to 552 practicing Catholic women: a bare 0.004% of all American Catholic women ages 15-44. Even without taking actual practice into account, the sample is still only 0.01% of Catholic women ages 15-44. The count drops far lower if we take into account all “Catholic women” in the US. It’s hard to imagine a data set that small being truly representative.
At first glance the numbers are quite clear:
Among Catholic women who have ever had sex, % that have ever used a contraceptive method other than natural family planning
1. They only regard Catholic women ages 15-44.
2. They only regard Catholic women who have had sex. The study acknowledges that there are Catholic women who haven’t, but doesn’t say how many.
3. “Catholic” as used here indicates any woman who said they are Catholic on the survey. Nonetheless, the study itself indicates that only 30% of those women go to church weekly. Although it notes that pre-marital sexual activity falls by more than 20% for practicing Christians, the Guttmacher study doesn’t supply any data on practicing Catholic women and contraception use.
4. Finally, the way the question is phrased (“% that have ever used a contraceptive method other that natural family planning”) forces a positive response for any use of contraception whatsoever. For example, there would be no difference between the case of Ms. A who took the pill on only one occasion 20 years ago, and Ms. B who is walking around with an IUD in her uterus right now. The survey isn’t indicative of the real situation as we speak.
The Guttmacher Institute was founded in 1968 as an integral part of Planned Parenthood’s corporate structure, and recieved its current name in 1977 to honor Dr. Alan Guttmacher—Planned Parenthood president from 1962 to 1974 and former president of the American Eugenics Society.