Sample
Survey 1 (baseline) 1996
More than 40,000 women responded to the baseline surveys for the main cohorts in 1996. Because of uncertainties about the accuracy of the Medicare database (which was used as the sampling frame for the stratified random samples), response rates cannot be exactly specified. It is estimated that 41%-42%, 53-56%, and 37-40% of the 1973-78 cohort, the 1946-51 cohort and the 1921-26 cohort, respectively, responded to the initial invitation to participate. Confidentiality restrictions meant that the names of the selected women were unknown to researchers. Usual methods of encouraging participation such as by telephone could not be used. The response rates were pleasing given that the invitation included a request for women to participate in the longitudinal study for up to 20 years.
In light of these response rates, it is important to assess any response bias so that the generalizability of the study findings can be determined. A comparison of the demographic characteristics of respondents and non-respondents was not possible because privacy guidelines prevented the researchers from having any information about women who were selected to receive an invitation but did not respond. We were able, however, to obtain aggregate data for non-respondents’ use of health services (from the Australian Medicare database). These data suggest that there are small differences in use of health services among respondents and non-respondents, with non-respondents less likely, for example, to have visited a medical specialist in the last 2 years (1946-51 cohort, 49% versus 54%; 1921-26 cohort, 65% versus 72%). There was not a significant difference in health service use between respondents and non-respondents from the 1973-78 cohort.
A proportion of this difference may be explained by the fact that some women who were selected may no longer be living in Australia or may have died, as the Medicare database is not routinely linked to emigration records or the National Death Index in Australia.
Although we were not able to ascertain reasons for non-response (because we were not allowed to know any details about the selected women), we were able, through comparison with the 1996 census data, to confirm that the participants in each of the cohorts are reasonably representative of the general population of women of the same age in Australia (Table 1). There is some response bias in terms of overrepresentation of women with tertiary education and underrepresentation of some groups of immigrant women.
Young
(18-23 years) WHA ABS % % |
Mid-age
(45-50 years) WHA ABS % % |
Older
(70-75 years) WHA ABS % % | ||||
---|---|---|---|---|---|---|
Number
|
14,762
|
759,680
|
14,072
|
734,155
|
12,804
|
377,152
|
Main current employment status
|
||||||
Employed full-time
|
31.3
|
32.4
|
36.1
|
36.0
|
NA
|
|
Employed part-time
|
19.2
|
26.4
|
30.1
|
28.5
|
NA
|
|
Worked (without pay)/ employed (other)
|
1.9
|
1.3
|
7.0
|
2.0
|
NA
|
|
Unemployed
|
6.4
|
10.5
|
1.9
|
4.0
|
NA
|
|
Total not in labour force
|
39.4
|
26.3
|
21.6
|
27.0
|
NA
|
|
Not stated
|
1.8
|
2.7
|
3.3
|
2.5
|
NA
|
|
Highest qualification completed
|
||||||
No post school qualification
|
69.8
|
69.3
|
63.1
|
61.8
|
79.8
|
70.4
|
Trade/Apprenticeship
|
2.4
|
7.9
|
3.5
|
7.0
|
3.7
|
2.7
|
Certificate/Diploma
|
15.1
|
6.0
|
15.9
|
8.7
|
7.3
|
3.3
|
University Degree
|
12.1
|
7.7
|
16.3
|
11.6
|
4.0
|
2.4
|
Other (not stated, inadequately described)
|
0.6
|
9.1
|
1.2
|
10.8
|
5.2
|
21.2
|
Aboriginal/Torres Strait Islander
|
||||||
Non indigenous
|
97.9
|
94.9
|
98.1
|
96.7
|
91.6
|
93.7
|
Aboriginal or TSI
|
1.6
|
2.7
|
0.8
|
1.1
|
0.3
|
0.4
|
Not stated
|
0.5
|
2.5
|
1.1
|
2.1
|
8.1
|
5.9
|
Country of birth
|
||||||
Australia
|
88.6
|
77.8
|
69.0
|
62.6
|
68.5
|
66.4
|
Other English speaking
|
3.5
|
4.1
|
13.9
|
11.6
|
12.4
|
11.0
|
Other Europe
|
1.3
|
1.6
|
8.7
|
11.0
|
9.7
|
12.7
|
Asia
|
3.6
|
10.6
|
4.3
|
8.2
|
1.8
|
3.3
|
Other/not stated
|
3.0
|
6.0
|
4.2
|
6.5
|
7.6
|
6.5
|
Present marital status
|
||||||
Married
|
8.2
|
9.0
|
75.1
|
73.0
|
54.7
|
48.9
|
Separated/divorced
|
0.0
|
1.1
|
13.2
|
18.7
|
6.3
|
6.8
|
Widowed
|
0.0
|
0.2
|
2.1
|
2.7
|
35.2
|
39.9
|
Never married
|
79.0
|
89.8
|
3.9
|
5.6
|
3.2
|
4.4
|
De Facto (not collected by ABS)
|
12.0
|
-
|
5.7
|
-
|
0.6
|
-
|
Present housing situation
|
||||||
House
|
74.3
|
79.4
|
84.7
|
89.2
|
76.7
|
79.3
|
Flat/apartment/unit
|
20.0
|
14.0
|
7.1
|
6.5
|
19.4
|
12.9
|
Other
|
5.7
|
6.6
|
8.2
|
4.3
|
3.9
|
7.9
|
The above table and information are taken from:
Brown, W. J., Dobson, A. J., Bryson, L., & Byles, J. E. (1999). The Australian Longitudinal Study on Women’s Health: on the progress of the main cohort studies. Journal of Women's Health & Gender-Based Medicine, 8(5), 681-688.
Sample for the longitudinal study of the 1973-78, 1946-51 and 1921-26 cohorts
Some participants completed Survey 1 in 1996 and did not provide any contact details (532 women from the 1973-78 cohort, 383 women from the 1946-52 cohort and 508 women from the 1921-26 cohort). Also, a very small number of women have alerted the study that they were not eligible by their birth date and they have been removed. Hence the numbers of women actually enrolled in the Australian Longitudinal Study on Women's Health (ALSWH) were 14,247 women in the 1973-78 cohort, 13,714 women in the 1946-51 cohort and 12,432 women in the 1921-26 cohort (Lee, C., Dobson, A. J., Brown, W. J., Bryson, L., Byles, J., Warner-Smith, P., & Young, A. F. (2005). Cohort Profile: the Australian Longitudinal Study on Women's Health. International Journal of Epidemiology, 34(5), 987-991).
1973-78 cohort
Table 2: Participation and retention of 14,247 women in the 1973-78 cohort of women who were 18-23 years old at the first survey in 1996*
Survey |
Survey 2 |
Survey 3 |
Survey 4 |
Survey 5 |
Survey 6 |
Survey 7 |
---|---|---|---|---|---|---|
Deceased |
22 |
33 |
50 |
58 |
77 |
102 |
Frailty (e.g. intellectual disability) |
3 |
9 |
12 |
15 |
16 |
16 |
Withdrawn |
230 |
518 |
800 |
951 |
1157 |
1436 |
Total ineligible |
255 |
560 |
862 |
1024 |
1250 |
1554 |
Contacted but did not return survey |
1332 |
653 |
1371 |
1994 |
1455 |
1399 |
Unable to contact participant |
2972 |
3953 |
2869 |
3030 |
3533 |
4108 |
Total non-respondents |
4304 |
4606 |
4239 |
5024 |
4988 |
5507 |
Respondents completed survey |
9688 |
9081 |
9145 |
8199 |
8009 |
7186 |
Eligible at current survey |
13,992 |
13,687 |
13,385 |
13,223 |
12,997 |
12693 |
Response rate as % eligible |
69.2% |
66.3% |
68.3% |
62.0% |
61.6% |
56.6% |
*data known as at July 2018
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 3). 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).
Table 3: Participation and retention of 13,715 women in the 1946-51 cohort of women who were 45-50 years old at the first survey in 1996*
Survey |
Survey 2 |
Survey 3 |
Survey 4 |
Survey 5 |
Survey 6 |
Survey 7 62-67 |
Survey 8 |
Deceased |
50 |
119 |
216 |
328 |
474 |
673 |
871
|
Frailty (e.g. dementia, stroke) |
7 |
23 |
34 |
51 |
70 |
100 |
120 |
Withdrawn |
209 |
424 |
622 |
870 |
1108 |
1651 |
2005 |
Total ineligible |
266 |
566 |
872 |
1249 |
1652 |
2424 |
2996 |
Contacted but did not return survey |
254 |
997 |
886 |
995 |
1148 |
1051 |
714 |
Unable to contact participant |
856 |
925 |
1051 |
832 |
903 |
1088 |
1382 |
Total non-respondents |
1110 |
1922 |
1937 |
1827 |
2051 |
2139 |
2096 |
Respondents completed survey |
12,338 |
11,226 |
10,905 |
10,638 |
10,011 |
9,151 |
8,622 |
Eligible at current survey |
13,448 |
13,148 |
12,842 |
12,465 |
12,062 |
11,290 |
10,718 |
Retention rate as % eligible |
91.7% |
85.4% |
84.9% |
85.3% |
83.0% |
81.1% |
80.4% |
*data known as at July 2018
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 4). 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.
Table 4: 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*
Survey |
Survey 2 |
Survey 3 |
Survey 4 |
Survey 5 |
Survey 6 |
Deceased |
549 |
1237 |
2287 |
3623 |
5282 |
Frailty (e.g. dementia, stroke) |
95 |
303 |
525 |
596 |
791 |
Withdrawn |
563 |
1090 |
1361 |
1372 |
1345 |
Total ineligible |
1207 |
2630 |
4173 |
5591 |
7418 |
contacted but did not return survey |
481 |
861 |
592 |
640 |
862 |
unable to contact participant |
310 |
295 |
509 |
641 |
97 |
Total non-respondents |
791 |
1156 |
1101 |
1281 |
959 |
Respondents completed survey |
10,434 |
8,646 |
7,158 |
5,560 |
4,055 |
Eligible at current survey |
11,225 |
9,802 |
8,259 |
6,841 |
5,014 |
Retention rate as % eligible |
93.0% |
88.2% |
86.7% |
81.3% |
80.9% |
*data known as at April 2018
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. Table 5 shows the numbers of eligible participants and respondents at end of each six month period. Response rates have been consistently above seventy percent.
Table 5: Participation in 6-month follow up surveys of the 12,432 women in the 1921-26 cohort (from November 2011 onwards)*
May 2012 |
Nov 2012 |
May 2013 |
Nov 2013 |
May 2014 |
Nov 2014 |
May 2015 | Nov 2015 | May 2016 | Nov 2016 |
May 2017 |
Nov 2017 |
May 2018 |
July |
|
Deceased |
5,532 | 5927 | 6,227 | 6,620 | 6,947 | 7,288 | 7,617 | 7,962 | 8,261 | 8,591 | 8,873 | 9,203 | 9,302 | 9304 |
Withdrawn |
2,334 | 2,363 | 2,409 | 2,347 | 2,294 | 2,181 | 2,102 | 1,967 | 1,875 | 1,740 | 1,678 | 1,534 | 1,546 | 1570 |
Total ineligible |
7,866 | 8,290 | 8,636 | 8,967 | 9,241 | 9,469 | 9,719 | 9,929 | 10,136 | 10,331 | 10,551 | 10,737 | 10,848 | 10874 |
Non-respondent |
1,136 |
882 |
954 |
992 |
1,073 |
999 |
987 | 979 | 934 | 854 | 819 | 716 | 707 | 1155 |
Respondent |
3,430 | 3,260 | 2,842 | 2,473 | 2,118 | 1,964 | 1,726 | 1,524 | 1,362 | 1,247 | 1,062 | 979 | 877 | 403 |
Total eligible |
4,566 | 4,142 | 3,796 | 3,465 | 3,191 | 2,963 | 2,713 | 2,503 | 2,296 | 2,101 | 1,881 | 1,695 | 1584 | 1558 |
Response rate as % of eligible |
75.1% | 78.7% | 74.9% | 71.4% | 66.4% | 66.3% | 63.6% | 60.9% | 59.3% | 59.4% | 56.5% | 57.8% | 55.4% | 25.9% |
* using 6MF questionnaires logged by 31st July 2018; this 6MF collection period is still open for respondents.
Comparison of the cohorts with Australian Censuses in 2001, 2006 and 2011
Demographic characteristics (Indigenous status, country of birth, marital status, lone person household, education, and employment) of respondents at each of the surveys have been compared with those of women of the same age in the Australian population, using data from the Australian Census conducted closest to the survey (see (1) Powers, J. (2004) Comparison of the Australian Longitudinal Study on Women’s Health cohorts with women of the same age in the 2001 Census. Technical Report. Newcastle: ALSWH. At: WHAvsCensus2001Feb2004; (2) Australian Longitudinal Study on Women’s Health (2009). Comparison of the ALSWH cohorts with women of the same ages in the 2006 Census and the 2004/2005 National Health Survey. In: Technical Report No. 32. 111-142; (3) Australian Longitudinal Study on Women’s Health (2013). Comparison of the ALSWH cohorts with women of the same ages in the 2011 Census. In: Technical Report No. 36. 107-135. As was found previously, there was some over-representation of Australian-born women and of women with tertiary education. In addition, ALSWH participants were more likely to be married, be employed and work longer hours than women of the same age in the general population. Some of these differences will be due to differences in the questions asked and the sampling frame i.e. to be selected for ALSWH women must have a Medicare card.
Longitudinal sample for the 1989-95 cohort
In 2012 and 2013, 17011 18-23 year old women were enrolled in the 1989-95 cohort. Women were mainly recruited using the internet and social media platforms. Consistent with the other cohorts, women were required to have a Medicare card. Women completed the online survey and provided consent to linkage of survey data with administrative databases such as Medicare.
Due to this different method of recruiting it was not possible to provide a response rate. Therefore it was necessary to compare the representativeness of the sample with women of the same age in the closest Australian Census (see Table 6). The 1989-95 cohort were broadly representative in terms of area of residence, State and Territory distribution, marital status and age distribution. Women with tertiary education were over-represented.
Table 6: Comparison of sociodemographic characteristics of the 1989-95 cohort of women aged 18 to 23 in 2013 with women of the same age range in the 2011 Australian Census
Table 6.1: Age
Age |
1989-95 cohort 2013 (n=17,069) % |
2011 Census (N=847,042) % | |
---|---|---|---|
18 |
15.2 |
16.0 |
|
19 |
17.5 |
16.2 |
|
20 |
17.2 |
16.8 |
|
21 |
16.5 |
17.1 |
|
22 |
16.9 |
17.0 |
|
23 |
16.7 |
17.0 |
Table 6.2: State/territories
1989-95 cohort 2013 (n=17,069) % |
2011 Census (N=847,042) % | ||
---|---|---|---|
New South Wales |
27.8 |
31.0 |
|
Victoria |
24.0 |
25.4 |
|
Queensland |
22.3 |
20.6 |
|
Western Australia |
11.0 |
10.6 |
|
South Australia |
7.6 |
7.3 |
|
Australian Capital Territory |
3.3 |
2.0 |
|
Tasmania |
2.9 |
2.1 |
|
Northern Territory |
0.8 |
1.0 |
Table 6.3: Area of residence
1989-95 cohort 2013 (n=17,069) % |
2011 Census (N=847,042) % | ||
---|---|---|---|
Major city |
75.3 |
74.5 |
|
Inner regional |
16.6 |
16.0 |
|
Outer regional |
6.7 |
7.2 |
|
Remote |
0.8 |
1.1 |
|
Very remote Migratory/no usual address |
0.3 N/A |
0.9 0.3 |
|
Missing |
0.3 |
- |
Table 6.4: Highest Qualification
1989-95 cohort 2013 (n=17,069) % |
2011 Census (N=847,042) % | ||
---|---|---|---|
Less than Year 12 |
7.4 |
14.9 |
|
Year 12 or equivalent |
43.0 |
46.1 |
|
Certificate / Diploma |
25.9 |
21.7 |
|
University degree |
22.5 |
9.4 |
|
Missing/not stated/inadequately described |
1.2 |
7.8 |
Table 6.5: Aboriginal or Torres Strait Islander origin*
1989-95 cohort 2013 (n=17,069) % |
2011 Census (N=847,042) % | ||
---|---|---|---|
No |
97.3 |
91.9 |
|
Yes |
2.7 |
3.4 |
|
Missing |
0.0 |
4.7 |
Table 6.6: Marital Status
1989-95 cohort 2013 (n=17,069) % |
2011 Census (N=847,042) % | ||
---|---|---|---|
Never married |
95.5 |
94.5 |
|
Married |
3.0 |
4.9 |
|
Separated/divorced/widowed |
0.4 |
0.6 |
|
Missing |
1.2 |
- |
*n=14,909 as this question was only asked in a later version of the survey
Table 7: Participation and retention of 17,011 women in the 1989-95 cohort of women who were aged 18-23 years at Survey 1 in 2013*
Survey |
Survey 2 |
Survey 3 |
Survey 4 |
Survey 5 |
Deceased |
1 | 6 | 8 | 13 |
Frailty (e.g. mental impairment) |
1 | 1 | 1 | 1 |
Withdrawn |
681 | 694 | 1744 | 1943 |
Total ineligible |
683 | 701 | 1753 | 1957 |
contacted but did not return survey |
2362 | 3879 | 1850 | 1813 |
unable to contact participant |
2622 | 3470 | 4400 | 4745 |
Total non-respondents |
4985 | 7350 | 6250 | 6558 |
Respondents completed survey |
11,344 | 8,961 | 9,007 | 8495 |
Eligible at current survey |
16,328 | 16,310 | 15,257 | 15053 |
Response rate as % eligible |
69.5% | 54.9% | 59.0% | 56.4% |
*data known as at July 2018