"Also selecting only those known to be affected by domestic violence may exclude those unable to disclose domestic violence... ?"
I think that is one of the most important aspects of dealing with domestic violence. A lot of people are ashamed to come forward. No one wants to incriminate loved ones. It often takes years for victims to finally find the courage and/or reach a point where they do not want to continue with that kind of abusive relationship anymore. It is even worse when the victims are children.
