Methods
Introduction
In 2005 and 2006, the NSW Department of Health, in conjunction with the area health services, completed the fourth and fifth years of the New South Wales Population Health Survey, an ongoing survey of the health of people of New South Wales using computer assisted telephone interviewing (CATI). The main aims of the survey are: to provide detailed information on the health of the people of New South Wales; and to support the planning, implementation, and evaluation of health services and programs in New South Wales.
Prior to the inclusion of the child component in the New South Wales Population Health Survey in 2003, the Centre for Epidemiology and Research conducted a child health survey in 2001. The reporting plan for the continuous survey includes a biennial report on child health for the whole state and the first report on child health from that continuous survey reported data from 2003 and 2004.
This section describes the methods used for the 2005-2006 Report on Child Health from the New South Wales Population Health Survey, which reports the health of residents aged 0-15 years.
New South Wales Population Health Survey
Survey instrument
The survey instrument was developed by the NSW Health Survey Program in consultation with key stakeholders, area health services, other government departments, and a range of experts. The survey included questions used in previous surveys and new questions developed specifically for 2005 and 2006. All new questions not previously used were submitted to the Ethics Committee of the NSW Department of Health for approval, and were field-tested prior to inclusion in the survey. The instrument was translated into 5 languages: Arabic, Chinese, Greek, Italian and Vietnamese.
Survey sample
In 2005 and 2006, the target population for the child component of the New South Wales Population Health Survey was all children aged 0-15 years living in households with private telephones. For each year, the target sample comprised approximately 475 children in each of the 8 area health services (total sample of 7,600 over 2 years).
The sampling frame was developed as follows. Records from the Australia on Disk electronic white pages (phone book) were geo-coded using MapInfo mapping software.[1,2] The geo-coded telephone numbers were assigned to statistical local areas and area health services. The proportion of numbers for each telephone prefix by area health service was calculated. All prefixes were expanded with suffixes ranging from 0000 to 9999. The resulting list was then matched back to the electronic phone book. All numbers that matched numbers in the electronic phone book were flagged and the number was assigned to the relevant geo-coded area health service. Unlisted numbers were assigned to the area health service containing the greatest proportion of numbers with that prefix. Numbers were then filtered to eliminate contiguous unused blocks of greater than 10 numbers. The remaining numbers were then checked against the business numbers in the electronic phone book to eliminate business numbers. Finally, numbers were randomly sorted. Households were contacted using random digit dialling. One person from the household was randomly selected for inclusion in the survey.
Interviews
In 2005 and 2006, interviews were carried out continuously between February and December. Selected households that had addresses in the electronic phone book were sent a letter describing the aims and methods of the survey 2 weeks prior to initial attempts at telephone contact. An 1800 freecall contact number was provided for potential respondents to verify the authenticity of the survey and to ask any questions regarding the survey. Trained interviewers at the Health Survey Program CATI facility carried out interviews. Up to 7 calls were made to establish initial contact with a household, and 5 calls were made in order to contact a selected respondent. If the selected respondent was a child under the age of 16 years, a parent or carer was selected as a proxy respondent.
Call outcomes and response rates
In total, 4,578 interviews were conducted with parents or carers of children aged 0-15 years, with 652 in the Sydney South West Health area, 466 in the South Eastern Sydney & Illawarra Health area, 672 from the Sydney West area, 504 Northern Sydney & Central Coast Health area, 612 fron Hunter & New England Health area, 525 from North Coast Health area, 571 from Greater Southern Health area, 576 from Greater Western Health area. The overall response rate was 58.4 per cent (completed interviews divided by completed interviews and refusals).
Data analysis
For analysis, the survey sample was weighted to adjust for differences in the probabilities of selection among subjects. These differences were due to the varying number of people living in each household, the number of residential telephone connections for the household, and the varying sampling fraction in each health area.
Post-stratification weights were used to reduce the effect of differing non-response rates among males and females and different age groups on the survey estimates. These weights were adjusted for differences between the age and sex structure of the survey sample and the Australian Bureau of Statistics 2002 mid-year population estimates (excluding residents of institutions) for each area health service. Further information on the weighting process is provided elsewhere.[3]
The SURVEYMEANS procedure in SAS was used to analyse the data and calculate point estimates and 95 per cent confidence intervals for the estimates. The SURVEYMEANS procedure calculates standard errors adjusted for the design effect factor or DEFF (the variance for a non-random sample divided by the variance for a simple random sample). It uses the Taylor expansion method to estimate sampling errors of estimators based on the stratified random sample.[4]
The 95 per cent confidence interval provides a range of values that should contain the actual value 95 per cent of the time. In general, a wider confidence interval reflects less certainty in the estimate for that indicator. The width of the confidence interval relates to the differing sample size for each indicator. Wide confidence bands mean that although there may be a large difference between the estimates, because of the small sample size in some indicators the difference is not significantly different.[4] For a pairwised comparison of subgroup estimates, the p-value for a two-tailed test was calculated using the normal distribution probability function PROBNORM in SAS, assuming approximate normal distribution of each individual subgroup estimates with the estimated standard errors, and approximate normal distribution for the estimated difference.
Indices of geographic remoteness and socioeconomic disadvantage: ARIA and SEIFA
The Accessibility-Remoteness Index of Australia Plus (ARIA+) is the standard Australian Bureau of Statistics (ABS) endorsed measure of remoteness.[5] It is derived using the road distances from populated localities to the nearest service centres across Australia. For each locality, the accessibility to services is expressed as a continuous measure from 0 (high accessibility) to 15 (high remoteness) and grouped into 5 categories: major cities, inner regional, outer regional, remote, and very remote.
The Socio-Economic Indexes for Areas (SEIFA) describe the socioeconomic aspects of geographical areas in Australia, using a number of underlying variables such as family and household characteristics, personal educational qualifications, and occupation.[6] The SEIFA index used to provide breakdowns of the New South Wales Population Health Survey data is the Index of Relative Socio-Economic Disadvantage. This index is calculated on attributes such as low income and educational attainment, high unemployment, and people working in unskilled occupations. The SEIFA index values are grouped into 5 quintiles, with quintile 1 being the least disadvantaged and quintile 5 being the most disadvantaged.
Both the ARIA+ and SEIFA indexes were assigned to the results of the New South Wales Population Health Survey in 2005 and 2006 based on respondents' postcode of residence.
Calculation of urban and rural
In this report, the term urban means the respondent lived in 1 of the 4 area health services designated as metropolitan: Northern Sydney & Central Coast, South Eastern Sydney and Illawarra, Sydney South West, and Sydney West. The term rural means the respondent lived in 1 of the 4 area health services designated as rural: Greater Southern, Greater Western, Hunter & New England, and North Coast.
Survival analysis
The LIFETEST procedure in SAS version 8.02 was used to perform survival analysis on breastfeeding data.[4] Survival analysis models data that specifies a time between an initial event and a terminating event. The initial event was the commencement of breastfeeding. The terminating event was the cessation of breastfeeding or the date of the survey. The length of time infants received any breastfeeding, full breastfeeding, and exclusive breastfeeding were modelled. The time infants were exclusively breastfed was determined from the date breastfeeding started (initial event) to the introduction of either solids, a milk substitute, water, juice, stopped breastfeeding, or the date of the survey (terminating event). The time infants were fully breastfed was determined from the date breastfeeding started (initial event) to the introduction of either solids, a milk substitute, stopped breastfeeding, or the date of the survey (terminating event). The survival analysis calculated non-parametric estimates of the survival distribution function using the life table method. The procedure calculated proportions at time intervals and 95 per cent confidence intervals using the weights that were rescaled to the survey sample.
Family functioning
Family functioning was measured using the McMaster Family Assessment Device, a 53-item tool arranged within 7 scales: problem solving, communication, roles, affective responsiveness, affective involvement, behaviour control, and general functioning.[7] The general functioning scale is a self-reported measure that describes the structural and organizational properties of the family group and the patterns of transactions among family members.[8] The scale has good reliability and validity and is recommended for use in assessing overall family functioning rather than specific dimensions of family functioning.[7,8] The scale generates a score between 1 and 4, with 1 reflecting healthy family functioning and 4 reflecting unhealthy family functioning. Unhealthy family function relates to avoiding discussing concerns or fears, having lots of bad feelings within the family, not being able to turn to each other for support or to confide in each other, not being able to talk about sadness or express feelings to each other, difficulty in making decisions, not accepting family members as they are, and difficulty planning family activities.[7,8]
Mental health
Child mental health was measured using the Strengths and Difficulty Questionnaire (SDQ), created by Professor Robert Goodman in the United Kingdom. The SDQ was identified as an appropriate tool and adapted for use in telephone surveys in consultation with Professor Goodman. It is a brief behavioural screening questionnaire for children aged 4-15 years that can be completed by parents or carers, children, or teachers. The questionnaire asks about 25 attributes divided into 5 scales: emotional symptoms, conduct problems, hyperactivity and inattention, peer relationship problems, and prosocial behaviour. The first 4 subscales (emotional symptoms, conduct problems, hyperactivity and inattention, and peer relationship problems) are calculated to give an overall total difficulties score between 0 and 40.[9,10] A child with a total difficulties score of 17 or above is considered to be at substantial risk of developing clinically significant behavioural problems.[10]
References
- Australia on Disk [software]. Sydney: Australia on Disk, 2000.
- MapInfo [software]. Troy, NY: MapInfo Corporation, 1997.
- Steel D, NSW Health Survey: Review of the Weighting Procedures. available online at: www.health.nsw.gov.au/public-health/survey/OtherPub/review_of_weighting_procedures.pdf, accessed 30 October 2007
- SAS Institute. The SAS System for Windows version 8.02. Cary, NC: SAS Institute Inc., 2001.
- Australian Bureau of Statistics. ASGC Remoteness Classification: Purpose and Use. Census Paper no. 03/01. Canberra: Australian Bureau of Statistics, 2003, available online at www.abs.gov.au, accessed 30 October 2007.
- Australian Bureau of Statistics. 2001 Census of Population and Housing: Socio-Economic Indexes for Areas, Information Paper, Catalogue no. 2039.0. Canberra: Australian Bureau of Statistics, 2003.
- Epstein N, Baldwin L, Bishop D. The McMaster Family Assessment Device. Journal of Marital and Family Therapy 1983; 9: 171-180.
- Byles J, Byrne C, Boyle M, Offord D. Ontario Child Health Study: Reliability and Validity of the General Funtioning Subscale of the McMaster Family Assessment Device. Family Process, 1988, 27: 97-104.
- Goodman R. The Strengths and Difficulties Questionnaire: A Research Note. Journal of Child Psychology and Psychiatry 1997; 38: 581-586.
- Youth in Mind. Information for researchers and professionals about the Strengths & Difficulties Questionnaires online at www.sdqinfo.com, accessed 30 October 2007.
| Source: | New South Wales Population Health Survey 2006 (HOIST). Centre for Epidemiology and Research, NSW Department of Health. |
| Print version: | Although this page can be printed directly from your web browser, a higher quality version is available as a PDF file that can be printed or viewed on screen. |
| Produced by: | Centre for Epidemiology and Research, Population Health Division, NSW Department of Health. |
| Last updated on: | 25 January 2008 |