1946-51 cohort
Retention has been much higher among the 1946-51 cohort of women; 92% responded to Survey 2 in 1998, 85% responded to Survey 3 in 2001, Survey 4 in 2004 and Survey 5 in 2007, and 83% responded to Survey 6 in 2010, 81% to Survey 7 in 2013 and 80% to Survey 8 in 2016 (See Table below). The major reasons for non-response among the 1946-51 cohort has been that the research team has been unable to contact the women (6% to 8% of eligible women between Survey 2 and Survey 6), and non-return of questionnaires by women who could be contacted (2% at Survey 2 and 7% to 10% of eligible women at subsequent surveys).
Participation and retention of 13,714 women in the 1946-51 cohort of women who were 45-50 years old at the first survey in 1996
| Year Survey Age in years | 1998 Survey 2 47-52 | 2001 Survey 3 50-55 | 2004 Survey 4 53-58 | 2007 Survey 5 56-61 | 2010 Survey 6 59-64 | 2013 Survey 7 62-67 | 2016 Survey 8 65-70 | 2019 Survey 9 68-73 |
|---|---|---|---|---|---|---|---|---|
| Deceased | 50 | 119 | 216 | 329 | 475 | 675 | 878 | 1173 |
| Frailty (e.g. dementia, stroke) | 7 | 23 | 34 | 51 | 70 | 100 | 120 | 128 |
| Withdrawn | 209 | 424 | 622 | 869 | 1107 | 1649 | 2001 | 2081 |
| Total ineligible | 266 | 566 | 872 | 1249 | 1652 | 2424 | 2999 | 3382 |
| Contacted but did not return survey | 254 | 997 | 886 | 995 | 1148 | 1051 | 714 | 718 |
| Unable to contact participant | 856 | 925 | 1051 | 832 | 903 | 1088 | 1379 | 1658 |
| Total non-respondents | 1110 | 1922 | 1937 | 1828 | 2051 | 2139 | 2093 | 2376 |
| Respondents completed survey | 12338 | 11226 | 10905 | 10638 | 10011 | 9151 | 8622 | 7956 |
| Eligible at current survey | 13448 | 13148 | 12842 | 12465 | 12062 | 11290 | 10715 | 10332 |
| Retention rate as % eligible | 91.7% | 85.4% | 84.9% | 85.3% | 83.0% | 81.1% | 80.5% | 77% |