EXAMPLE 2 Write-in opinion polls

Ann Landers once asked the readers of her advice column, “If you had it to do over again, would you have children?” She received nearly 10,000 responses, almost 70% saying, “NO!” Can it be true that 70% of parents regret having children? Not at all. This is a voluntary response sample. People who feel strongly about an issue, particularly people with strong negative feelings, are more likely to take the trouble to respond. Ann Landers’s results are strongly biased—the percentage of parents who would not have children again is much higher in her sample than in the population of all parents.

On August 24, 2011, Abigail Van Buren (the niece of Ann Landers) revisited this question in her column “Dear Abby.” A reader asked, “I’m wondering when the information was collected and what the results of that inquiry were, and if you asked the same question today, what the majority of your readers would answer.”

Ms. Van Buren responded, “The results were considered shocking at the time because the majority of responders said they would NOT have children if they had it to do over again. I’m printing your question because it will be interesting to see if feelings have changed over the intervening years.”

In October 2011, Ms. Van Buren wrote that this time the majority of respondents would have children again. That is encouraging, but this was, again, a write-in poll.