Welcome to Women's Health Australia (WHA)

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 nonrespondents 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 nonrespondents’ 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 nonrespondents, with nonrespondents 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 nonrespondents 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.

Some women only 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). 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, 13,716 women in the 1946-51 cohort and 12,432 women in the 1921-26 cohort.

Table 2: Participation and retention of the 1973-78 cohort
		Survey 1	Survey 2	Survey 3	Survey 4
Age in years		18 - 23	22 - 27	25 - 30	28 - 33
Eligible at previous survey			14247	14116	13886
Ineligible
	deceased between surveys		22	10	15
	frailty (e.g. intellectual disability)		3	6	4
	withdrawn before mailout survey date		106	213	311
Total ineligible			131	229	330
Eligible at current survey			14116	13887	13557
Non-respondents
	withdrawn from the project		124	200	171
	contacted but did not return survey		1332	654	1372
	unable to contact participant		2972	3952	2869
Total non-respondents			4428	4806	4412
Respondents
	completed survey	14247	9688	9081	9145
Retention rate as % eligible			68.6%	65.4%	67.5%

Among the 1973-78 cohort, 69% responded to Survey 2 in 2000 and 65% to Survey 3 in 2003 and 67% have responded to Survey 4 in 2006 (Table 2). This retention compares well with other surveys of this highly mobile age group. The major reason for non-response among the 1973-78 cohort was that the research team was unable to contact the women (21% of eligible women at Survey 2 and 28% at Survey 3 and 21% at Survey 4), despite using all possible methods of maintaining contact. Women in their twenties are characterised by high levels of mobility, change of surnames on marriage, often not having telephone listings and not being registered to vote and making extended trips outside Australia for work, education or recreation.

Demographic characteristics (country of birth, marital status, education, employment and lone person household) of these respondents at Survey 1 (1996) and Survey 2 (2000) were compared with those of women of the same age in the Australian population, using data from the 1996 and 2001 Censuses respectively. The comparisons revealed few differences however there was some under-representation of women from non-English language countries at both surveys, a not unexpected finding given that Medicare routinely excludes overseas students. The disparity in education increased between 1996 and 2001. Whereas at the 1996 Census almost 70% of young women had no post school qualifications (ALSWH and the general population), 31% and 49% had no post school qualifications in the ALSWH sample in 2000 and the 2001 Census respectively. Some of these differences will be due to overseas graduates returning home and Australian graduates working overseas. ALSWH women were less likely to be employed compared to women of the same age in the 1996 Census (52% versus 60%) but more likely to be employed than women of the same age in the 2001 Census (85% versus 67%).

Retention has been much higher among the 1946-51 cohort; 91% responded to Survey 2 in 1998 and 84% responded to Survey 3 in 2001 and Survey 4 in 2004 (Table 3) and survey 5 in 2007. The major reasons for non-response among the 1946-51 cohort was that the research team was unable to contact the women (6%, 7%, 8% and 7% of eligible women at Survey 2, Survey 3 and Survey 4 respectively) and non-return of questionnaires by women who could be contacted (2%, 8% and 7% of eligible women at Survey 2, Survey 3, Survey 4 and Survey 5 respectively) and non return of questionnaires by women who could be contacted (2%, 8%, 7% and 8% of eligible women at the second, third, fourth and fifth surveys). Middle aged women typically lead busy lives often working, as well as caring for parents and their children. The women who could not be contacted were more likely to be separated, divorced or widowed.

Data from the 1996 and 2001 Censuses were used to compare demographic characteristics (country of birth, marital status, education, employment and lone person household) of women of the same age in the Australian population with respondents at Survey 1 (1996) and Survey 3 (2001). There were few differences, however there was some under-representation of women from non-English language countries and women who were separated or divorced at both surveys.

Of the 1921-26 cohort, 91% responded to Survey 2 in 1999 and 85% to Survey 3 in 2002, 91% to Survey 4 in 2005 and 79% to Survey 5 in 2008 (Table 4). Among these women the major reason for non-response was non-return of the questionnaire (4%, 8%, 7% and 9% of eligible women at Surveys 2, 3, 4 and 5 respectively) although increasingly the participant can not be contacted (3% at Surveys 2 and 3, 6% at Survey 4 and 9% at Survey 5). Non-respondent women tended to report poorer self-rated health at Survey 1 than respondents.

Demographic characteristics (country of birth, marital status, education and lone person household) of the respondents at Survey 1 (1996) and Survey 3 (2002) were compared with those of women of the same age in the Australian population, using data from the 1996 and 2001 Censuses respectively. Comparisons showed few differences. There was some under-representation of women from non-English speaking countries in the ALSWH sample at both surveys. Comparisons are difficult for marital status and educational qualifications due to the high level of missing data in the Census.