This cohort was born between 1973 and 1978, and they were 18-23 years old at the first survey in 1996. Among the 1973-78 cohort, 69% responded to Survey 2 in 2000, 66% to Survey 3 in 2003, 68% responded to Survey 4 in 2006, 62% to Survey 5 in 2009, 62% to Survey 6 in 2012, and 57% responded to Survey 7 in 2015. This retention compares well with other surveys of this highly mobile age group. The major reason for non-response among the 1973-78 cohort is that that the research team has been unable to contact the women (between 21% and 32% of the cohort at subsequent surveys), despite using all possible methods of maintaining contact. Women in their twenties and thirties are characterised by high levels of mobility, change of surnames on marriage, often not having telephone listings, not being registered to vote, and making extended trips outside Australia for work, education, or recreation.