How was the GEO sample recruited and enrolled?
Approximately 30% of the sample was recruited through the Waisman Center Research Participation Core (RCP) at the University of Wisconsin-Madison. During recruitment, RCP provided lists on a monthly basis of all twins born at local hospitals. Around 40% of the sample was enlisted through the Wisconsin Vital Records Services. This office generated a list of all twin births in the state every six months, and GEO was allowed six months to contact and recruit families. The remaining families were recruited through the GEO website, word-of-mouth, flyers at OB/GYN offices, local news stories, Mothers of Multiples groups, and newspaper advertisements.
