Data source
Ten to Men is a national longitudinal study of boys and men aged 10 to 55 years. In waves spaced approximately 2–3 years apart, we will collect data on a range of life domains, including demographic and socio-economic characteristics, physical and mental health and wellbeing, health behaviours, and use and knowledge of health services. The baseline survey was conducted between October 2013 and July 2014. The total sample consisted of 15,988 males, who were sampled using a multi-stage, clustered, random sample design. All eligible males residing in private households were approached, with separate cluster samples drawn from regional strata in order to oversample males from regional areas. Data were collected from males 15 years and older using a self-completion questionnaire and by interview and parent self-completion questionnaire for boys aged 10 to 14 years. The response fraction was 35 %. Response rates for individual questions in the survey varied between 82 and 100 %. More details on the study can be found elsewhere [25].
The sample for this analysis consisted of 13,569 of the 13,884 participants aged 18 to 55 years and excluded those who did not report their age (0.9 %) or did not respond to the disability questions (1.4 %).
Disability variable
The Ten to Men survey included the Washington Group short set of questions on disability, a widely used instrument for measuring disability which has been validated in many countries [24]. It consists of six questions relating to core functional domains (seeing, hearing, walking, cognition, self-care and communication) with answers reported on a severity scale (no difficulty, some difficulty, a lot of difficulty and cannot do at all). We classified participants as having a disability if they reported that they had a lot of difficulty or cannot do at all on one or more of the core domains [24].
Other variables
The survey included questions on a range of demographic and socio-economic variables including age, race/ethnicity, relationship status, education, employment, housing, income and financial security. Age was classified into the following groups: 18 to 24, 25 to 34, 35 to 44, and 45 to 55 years. Variables measuring race/ethnicity included country of birth (Australia, other); language spoken at home (English, other); and Aboriginal and Torres Strait Islander (ATSI, not ATSI). Relationship status was coded as married or in a de facto relationship, separated or divorced or widowed, and single. Area of residence was defined as metropolitan, inner regional, and outer regional. Socio-economic variables included education (did or did not complete secondary school); household income (≥$150,000, $100,000 to $149,999, $50,000 to $99,999, $30,000 to $49,999, $1 to $29,999, nil or negative income), and labour force status (employed, unemployed and looking for work, and not in the labour force). If employed, occupation was classified according to skill level (high, medium and low skill); employment arrangements (permanent, fixed-term or casual, self-employed); number of hours worked; preference for hours worked in relation to current hours worked (about the right amount, prefer fewer hours, prefer more hours); access to paid leave (e.g. sick or annual leave) (yes, no); experienced shortage of money in the last 12 months (yes, no - based on whether they answered yes to one or more of six questions regarding financial security such as could not pay bills on time); housing tenure (outright owner, mortgagor, living in rental accommodation, other); and housing affordability (affordable, unaffordable - defined as paying more than 30 % of household income on accommodation).
Area-level socio-economic disadvantage was categorised using population quintiles of the Index of Relative Socio-economic Disadvantage (IRSD), measured at Statistical Area Level 1 (SA1), the smallest geographic unit in the Australian Standard Geographic Classification. The IRSD is a composite index that summarises a range of information about the economic and social conditions of the people living within specific geographic areas [26]. A low IRSD score indicates relatively greater disadvantage.
Social support was measured using eight questions relating to emotional and informational support developed for the Medical Outcomes Study [27]. The questions elicit the availability of different kinds of support, which is graded on a five point scale ranging from “none of the time” to “all of the time”. Responses to these questions were summed and described as a continuous variable. Social participation was measured using three variables: current active membership in a club or association (yes, no), participation in ongoing community service activities (yes, no), and frequency of attendance at events that bring people together, such as fetes, festivals and community events (very often/often/sometimes, rarely/never). Participants were also asked about any experience of discrimination over the past two years, which was coded as no (never) or yes (rarely, occasionally, fairly often, very often).
Several of the many measures of general health and wellbeing collected in Ten to Men were used in this analysis. The Physical Component Summary (PCS) and the Mental Component Summary (MCS) scores are summary measures of physical health and mental health, respectively, derived from the Short Form 12 (SF-12) health survey [28]. The summary scores are validated, psychometrically based measures that are standardised to a mean of 50 and standard deviation of 10, and a range from 0 (worst health) to 100 (best health). The Personal Wellbeing Index – Adult (PWI-A) is a multi-item scale which measures subjective wellbeing [29]. The PWI-A is based on responses to seven questions that measure satisfaction within specific life domains: standard of living, health, life achievements, personal relationships, safety, feeling part of a community, and future security. Responses are recorded on an 11-point Likert scale ranging from 0 (completely dissatisfied) to 10 (completely satisfied). We analysed the seven domains individually and in aggregate via the PWI-A, which is created by summing the seven items to yield an overall score of subjective wellbeing.
Statistical analysis
First, we calculated the population-weighted prevalence of disability among Australian men aged 18 to 55 years, by age group. We compared the patterns of demographic, social and economic variables between men with and without disabilities using proportions and means, and tested for differences using Chi squared and t tests respectively. To ensure that any differences in health and wellbeing between the groups were not confounded by systematic differences in the distribution of age, we also used population weighted linear regression analysis that adjusted for age.
The sample weights used in the weighted estimates (prevalence and age-adjusted health and wellbeing comparison) were calculated based on the inverse of the probability of selection at the level of the individual participant [30].
The number and proportion of missing observations for each variable are described in Additional file 1: Table S1.