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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 37-40%, 53-56% and 41%-42% of the 1921-26 cohort, the 1946-51 cohort and the 1973-78 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 generalisability 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 (1921-26 cohort, 65% versus 72%; 1946-51 cohort, 49% versus 54%). 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 over representation of women with tertiary education and under representation of some groups of immigrant women.

Sample of original 3 cohorts

Some participants completed Survey 1 in 1996 and did not provide any contact details (508 women from the 1921-26 cohort, 383 women from the 1946-52 cohort and 532 women from the 1973-78 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 12,432 women in the 1921-26 cohort 14,247, 13,714 women in the 1946-51 cohort and women in the 1973-78 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).

Table 1: Socio-demographic characteristics

Main current employment status1973-78 cohortABS 18-23 years1946-51 cohortABS 45-50 years1921-28 cohortABS 70-75 years
Number of respondents14,762759,68014,072734,15512,804377,152
Employed full-time (%)31.332.41.36.136N/AN/A
Employed part-time (%)19.226.430.128.5N/AN/A
Worked (without pay) /
employed (other) (%)
1.91.37.02.0N/AN/A
Unemployed (%)6.410.51.94.0N/AN/A
Total not in labour force (%)39.426.321.627.0N/AN/A
Not stated (%)1.82.73.32.5N/AN/A
Highest qualification completed1973-78 cohortABS 18-23 years1946-51 cohortABS 45-50 years1921-28 cohortABS 70-75 years
Number of respondents14,762759,68014,072734,15512,804377,152
Australia (%)88.677.869.062.668.566.4
Other English speaking (%)3.54.113.911.612.411.0
Other Europe (%)1.31.68.711.09.712.7
Asia (%)3.610.64.38.21.83.3
Other/not stated (%)3.06.04.26.57.66.5
Aboriginal/Torres Strait Islander1973-78 cohortABS 18-23 years1946-51 cohortABS 45-50 years1921-28 cohortABS 70-75 years
Number of respondents14,762759,68014,072734,15512,804377,152
Non indigenous (%)97.994.998.196.791.693.7
Aboriginal or TSI (%)1.62.70.81.10.30.4
Not stated (%)0.52.51.12.18.15.9
Country of birth1973-78 cohortABS 18-23 years1946-51 cohortABS 45-50 years1921-28 cohortABS 70-75 years
Number of respondents14,762759,68014,072734,15512,804377,152
No post school qualification (%)69.869.363.161.879.870.4
Trade/Apprenticeship (%)2.47.93.57.03.72.7
Certificate/Diploma (%)15.16.015.98.77.33.3
University Degree (%)12.17.716.311.64.02.4
Other (not stated,
inadequately described) (%)
0.69.11.210.85.221.2
Present marital status1973-78 cohortABS 18-23 years1946-51 cohortABS 45-50 years1921-28 cohortABS 70-75 years
Number of respondents14,762759,68014,072734,15512,804377,152
Married (%)8.29.075.173.054.748.9
Separated/divorced (%)0.01.113.218.76.36.8
Widowed (%)0.00.22.12.735.239.9
Never married (%)79.089.83.95.63.24.4
De Facto (not collected by ABS) (%)12.05.70.6
Present housing situation1973-78 cohortABS 18-23 years1946-51 cohortABS 45-50 years1921-28 cohortABS 70-75 years
Number of respondents14,762759,68014,072734,15512,804377,152
House (%)74.379.484.789.276.779.3
Flat/apartment/unit (%)20.014.07.16.519.412.9
Other (%)5.76.68.24.33.97.9

Table 1: Socio-demographic characteristics for the young, mid-age and older respondents and for women of the same age in the general population (ABS). The above tables 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.

Comparison of original cohorts with Australian Censuses

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.

  • 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. In: Technical Report February 2004.
  • 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.
  • 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.

Cohort participation and retention