Won't Miss #299 - missing sisters

Part of my freelance work is doing English telephone testing. One of the questions I ask in order to elicit as much speaking as possible from my subjects is, "tell me about your family." In 90% of cases, if someone has a sister who is already married, they won't even mention her existence unless I specifically ask "do you have a sister?" In the other 10% of cases, they'll say, "I have a sister,