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1921-26 cohort

Of women from the 1921-26 cohort, 93% responded to Survey 2 in 1999, 88% to Survey 3 in 2002, 87% to Survey 4 in 2005, 81% to Survey 5 in 2008 and to Survey 6 in 2011 (See Table below). Among the 1921-26 cohort the major reason for non-response was non-return of the questionnaire, rising from 4% at Survey 2 to 17% at Survey 6 although up to 9% of participants could not be contacted. Non-respondent women tended to report poorer self-rated health at Survey 1 than respondents. The effects of these losses were evaluated in terms of losses due to death and non-death (Brilleman, S. L., Pachana, N. A., & Dobson, A. J. (2010). The impact of attrition on the representativeness of cohort studies of older people. BMC Medical Research Methodology, 10. doi: 7110.1186/1471-2288-10-71). Brilleman et al. concluded that non-death losses were potentially a greater source of bias than effects of death.

Participation and retention of 12,432 women in the 1921-26 cohort of women who were aged 70-75 years at Survey 1 in 1996

Age in years
Survey 2
Survey 3
Survey 4
Survey 5
Survey 6
Frailty (e.g. dementia, stroke)95303524593788
Total ineligible12072630417355927419
Contacted but did not return survey481861592640862
Unable to contact participant31029550964096
Total non-respondents791115611011280958
Respondents completed survey104348646715855604055
Eligible at current survey112259802825968405013
Retention rate as % eligible93.0%88.2%86.7%81.3%80.9%
Data known as at 27th July 2022

Six-month follow up surveys of the 1921-26 cohort

From November 2011, shorter surveys containing a set of core questions were mailed to the 1921-26 cohort every six months after the return of the previous survey. The Table below shows the numbers of eligible participants and respondents at the end of each six month period. Response rates have been consistently above seventy percent.

Participation in 6-month follow up surveys of the 12,432 women in the 1921-26 cohort

6M period endingMay 2012Nov 2012May 2013Nov 2013May 2014Nov 2014May 2015Nov 2015May 2016Nov 2016May 2017Nov 2017May 2018Nov 2018May 2019Nov 2019May 2020Nov 2020May 2021Nov 2021May 2022Nov 2022*
Total ineligible786782918638896992449472972199321013910334105541074310905110641120111328114491156111678117751182311846
Total eligible4565414137943463318829602711250022932098187816891527136812311104983871754657609586
Response rate as % of eligible75.1%78.7%74.9%71.4%66.4%66.3%63.7%61.0%59.4%59.4%56.5%58.0%57.4%56.1%51.7%52.5%49.8%46.4%44.0%41.4%36.7%33.1%
Status of 12,432 women from the 1921-26 cohort and at each 6MF questionnaire from November 2011 onwards. Using 6MF questionnaires logged by 31st October 2022. Response rate based on eligible participants only.
*This 6MF collection period is still open for respondents.