Respondents make answers unreliable; that is, their answers may or may not be correct and when all you have are answers it’s impossible to determine which, if any, are correct or incorrect. Zoë Heller, in her review of Jennifer Senior’s asking-based effort, All Joy and no Fun: The Paradox of Modern Parenthood, describes and explains the unreliability of the answers given by parents interviewed by Senior: “It’s possible, of course,that some parents are lying, or at least sentimentalizing the truth, when they offer up [their] sort of rosy `end-of-the-day’ verdict on parenthood. (There are strong social and emotional incentives for not publicly expressing remorse about one’s reproductive choices.)”
I’ve also reviewed Senior’s essentially worthless book on Amazon.com.
For a complete statement of how respondents make answers unreliable, see my book, The Problem with Survey Research.