LSAC exposures and covariates at wave 1 and their handling for this study
| Variable | Measure and additional information |
| Exposures | |
| Either parent highest education | Highest qualification and year of primary/secondary school completed by parents 1 and 2 were recorded. Highest level of education of either parent 1 and parent 2 was classified into three categories: ‘degree’ for parents who completed a postgraduate degree, graduate diploma/certificate or bachelor degree (including honours), regardless of the highest year of school that they completed, ‘completed school’ for participants who completed year 12 (ie, the last year of secondary school in Australia) or equivalent but did not have a university qualification and ‘did not complete school’ for participants who did not complete year 12 or equivalent and did not have a university qualification. |
| SEIFA neighbourhood disadvantage | This census based Australian Bureau of Statistics Index of Relative Socio-economic Disadvantage is a composite variable, as described previously.27 SEIFA neighbourhood disadvantage classified as quintiles, using sampling weights from wave 1. |
| SEP | At each wave, LSAC provides a widely used composite SEP variable that combines and averages information on parental occupational status, parental educational attainment and annual family income, described previously.28 SEP classified as quintiles, using sampling weights from wave 1. |
| Combined yearly income before tax | LSAC records the present yearly income before tax, superannuation or health insurance for parent 1 and their partner combined and included pensions and allowances. Response options classified into four categories: ‘<$26 000 per year’, ‘$26 000–$51 999 per year’, ‘$52 000–$103 999 per year’ and ‘$104 000 or more per year’. |
| Mean hours worked per week | Composite variable generated, specifically the sum of the average hours worked per week for parents 1 and 2. Average hours worked per week classified into five categories: ‘0’, ‘1–39’, ‘40–59’, ‘60–79’ and ‘80+’ hours per week for both parents combined. |
| Remoteness area | Based on the Australian Standard Geographical Classification remoteness structure39 and consists of three categories: ‘major cities’, ‘inner regional’ and ‘outer regional/remote/very remote’. |
| Home ownership | Home ownership status of the current home (house/flat/unit) in which the study child resides was recorded. Response options classified into four categories: ‘owned outright’, ‘being paid off’, ‘rented’ and ‘other’, The category ‘other’ consists of: ‘being purchased under a rent/buy scheme’, ‘occupied under a life tenure scheme’ and ‘none of these’. |
| Food security | Parent 1 was asked whether over the last 12 months, due to shortage of money, they had financial limits on the type of food they could buy. Response options dichotomised into: ‘yes’ and ‘no’. |
| Covariates | |
| Child age | In months (converted to years) |
| Child sex | Male/female |
| Child indigenous status | Parent 1 was asked whether the study child was of Aboriginal or Torres Strait Islander origin. Indigenous status dichotomised into: ‘yes’ for children who were of Aboriginal and/or Torres Strait Islander origin and ‘no’ for children who were not. |
| Child language other than English spoken at home | Parent 1 was asked whether the study child speaks a language other than English at home. Similar to Renzaho et al,40 we grouped languages into two categories: ‘English only’ and ‘Other language’. |
| Parent 1 or 2 age | The age last birthday for parents 1 and 2 was recorded. Parent 1 and 2 ages classified as: ‘<25’, ‘25–29’, ‘30–34’ and ‘35+’ for parent 1 in wave 1 of the B cohort; and ‘<30’, ‘30–34’, ‘35–39’ and ‘40+’ for parent 2 in wave 1 of the B Cohort, and parents 1 and 2 in wave 1 of the K Cohort. |
| Child number of older siblings | For both cohorts, the number of older siblings of the study child in the household was recorded. Response options classified as four categories: ‘none,’ ‘one,’ ‘two’ and ‘three or more’. |
| Singleton/multiple birth | Parent 1 was asked whether the study child was a single birth, a twin, a triplet or more. Response options dichotomised into: ‘single birth’ and ‘multiple birth’. |
B Cohort, Baby Cohort; K Cohort, Kindergarten Cohort; LSAC, Longitudinal Study of Australian Children; SEIFA, Socio-Economic Indexes for Areas; SEP, socioeconomic position.