This exercise encourages students to think critically about the statistics that they encounter in the media. Note: This data is about abortion. When I use this exercise, I stress to my students that the exercise isn't about being pro-choice or anti-abortion, it is about being anti-bad statistics.
Writer Sarah Kliff published an article in Newsweek about de-stigmatizing abortion. In the article, she makes the claim that 40% of American women have had abortions. Some readers questioned this estimate. This is her reply to those readers.
I challenge my students to find flaws or possible flaws/points of concern in the mathematics behind the 40% estimate. Some points that they come up with: a) The data doesn't include minors, b) the data doesn't include women who were alive between 1973 (Row v. Wade) and 2004 and but died/moved out of the US before the 2005 census data (which was used in her calculations), c) data estimates that about half of women having an abortion at any given time have had a previous abortion, d) the author has is pro-choice, which may or may not be an issue, and e) her data for total number of legal abortions comes from a pro-choice organization, which may or may not be an issue.
Again, my example isn't about pro-choice/anti-abortion, it is about judging the veracity of data being used for persuasion.
Final, in order to equally inflame my anti-abortion students, I like to follow this exercise up with this clip from The Daily Show with Jon Stewart in which Stewart rips apart anti-abortion (now former) Senator John Kyl for making up statistics in order to attack Planned Parenthood.