• The way this is reported on, and what precisely each number means are things you should investigate when they do not line up with your expectations. This chart comes from this data brief. In the definitions the following is stated (emphasis mine):

    In this report, as in prior NSFG reports (3), women who were currently using more than one method are classified by the method that was most effective in preventing pregnancy, because that method has the greatest impact on their risk of unintended pregnancy. For example, women who report using both oral contraceptive pills and male condoms in the current month are classified as using pills, because pills are more effective at preventing a pregnancy.

    • Aha, that does make some difference. For example, my girlfriend takes birth control pills due to health-related reasons (and as far as I can tell, this is moderately common), so even though we do use condoms we would not be counted. Sorry for being lazy on this one, and thank you for doing the work of researching this in more depth ^_^