Case-control studies of completed and attempted suicide in young people in NSW

1. Case-control studies of completed and attempted suicide in young people in NSW Richard Taylor1,2, Michael Dudley2, Greg Carter3, John Hilton4 Stephen Morrell2, Coletta Hobbs5, Andrew Page1 1. School of Population Health, University of Queensland 2. School of Public Health and Community Medicine, University of New South Wales 3. Discipline of Psychiatry, University of Newcastle 4. NSW Institute for Forensic Medicine 5. Sydney School of Public Health, University of Sydney

2. Disclaimer... • A case study frozen in time... • ...although questions still relevant • Case study written circa ≈ 2003-04 • Priority areas change • NHMRC funded

3. Background & rationale • Suicide major public health issue for young adults, particularly males • ‘youth suicide epidemic’ 1990s • as common as MVAs • Considerable person years of life lost • Suicide multidimensional phenomenon • individual, interpersonal, socio-economic, socio-cultural factors • Previous aetiological studies: • mostly of attempted suicide • mostly of adolescents • many not population-based and not generalisable to the whole community • too small to examine the contributions of both social factors and individual factors simultaneously • no studies like this conducted in Australia

4. Background & rationale • No Aust studies have considered: • both individual and socio-demographic factors simultaneously in young adults, including urban-rural differences • attempted and completed suicide together • explicitly investigated reasons for gender disparity • See summary lit review in example provided • Proposed an explanatory framework for young adult suicide to investigate individual and social factors together (see example proposal)

5. Primary objectives • To delineate and quantify risk factors and population characteristics of both suicide and attempted suicide in young people age 18-34 years from New South Wales across urban and rural areas • To elucidate predictors for completed suicide compared to those who attempt suicide • The main hypotheses for this project relate to the relative roles of modifiable socio-cultural factors (including isolation and unemployment); modifiable individual psychological/psychiatric factors; and modifiable precipitating factors and availability of means. Of interest is the magnitude of their effects, not just odds ratios (OR), but also attributable fractions (AF)

6. e.g. Hypotheses • Hypothesis 1: That although individual psychiatric/psychological factors may have higher odds ratios (OR) for suicide or attempted suicide than socio-economic factors, the latter have greater attributable fractions (AF), and therefore are of considerable importance. • Hypothesis 2: That young males will manifest higher suicide OR and AF than females for socio-economic factors and externalizing psychiatric factors (e.g. substance misuse, behaviour disorders), and young females will have higher OR and AF than males for internalizing psychological-psychiatric factors (e.g. anxiety, depression). • Hypothesis 3: That the socio-demographic and individual risk factors associated with suicide attempts are different from those associated with a completed suicide, and the difference will be greater for females than for males. • Hypothesis 4: That the socio-demographic and individual risk factors associated with suicide using community controls are different from risk factors using attempted suicide as controls, and these differences vary by gender. • Hypothesis 5: Individual and socio-economic risk factors and means for suicide and attempts will differ in importance by urban-rural residence and socio-economic group (defined by individual characteristics or by locality of residence). • Hypothesis 6: A ‘contextual’ effect of area-based socio-cultural and socio-economic measures will be evident over and above the effect of individual characteristics (including individual measures of socio-economic status)

7. Question of study design • Aetiological questions, so analytic design? • Preferably individual level study, not ecologic (although ecologic questions are involved) • deficiencies in previous studies, due to aggregate nature • individual-level studies feasible, from literature, but not focussed on young adults • Case-control, given rare outcome? • recall bias in exposure measurement. Exposure measurement important in this study. Especially given the critique of ‘psychological autopsy’ studies • logistical issues in selecting controls • Cohort study, prospective? • Stronger design, reduce recall bias, nice strong effect sizes between exposures and outcomes (e.g. depression RR>5) • But rare outcome (incidence of suicide ≈15/100,000), so HUGE numbers required despite large RRs • Maybe for attempted suicide? But we want to look at case-case comparisons too... • C-C seems the most reasonable option

8. Proposed study design • 2 population-based case-control studies • one of suicide, one of attempts, plus case-case • time efficient and cost effective, practical way to investigate the multi-dimensional factors • Case ascertainment and interviews will be embedded in existing counselling and treatment services. • Attempted suicides: • Cases enumerated through hospitals in catchment area • Controls enumerated through randomly selected Collection Districts (door knocking) • For completed suicides: • Cases enumerated through coronial information, next of kin contacted • Controls enumerated through randomly selected Collection Districts (door knocking), next of kin contacted

9. Study design: 2 case-control studies, 1 case-case study

10. Proposed study factors investigated • Demographics (including migrant status, place of residence, SES, religion etc.) • Attitudes to suicide and previous suicidal behaviour • Social activity and community factors • Recent life-events • Childhood and family upbringing • Personality factors • Disability • Health service utilisation • Mental illness (CIDI) • Family history of mental health problems and suicide

11. Proposed interview • Automated computer program using laptops, with 4 versions: • Interview for attempted suicide cases • Interview for attempted suicide controls • Informant interview for relatives/friends of suicide cases • Informant interview for relatives/friends of suicide controls • Questionnaire includes the CIDI, Life-Events questionnaire, Kessler 10+, EPQ among others • Conducted at a mutually convenient time and place for interviewer and participant • 1 hour in length for controls, 1-3 hours for cases

12. Sufficient sample size? • Based on a response rate of 80% (NZ, Hunter) • Based on proportion exposed of 20% • 12-month prevalence of ‘any’ mental disorder (NSMHWB) • To detect differences between exposed/not-exposed for RR≈1.5-2.00 at p=0.05 and Power of 80% • For attempted suicide: 562 cases, 562 controls • ratio of 1:1 • For completed suicide: 213 cases, 426 controls • ratio of 1:2 for males, 1:4 for females • Suicide much rarer, really rare in females, longer time to accrue (≈4 years) • Total N=3,442 • See table of ‘ranges’. Useful to present when RR estimates are unclear or arguable.

13. Recruitment procedure • Attempted suicide cases • Enumerated through hospital admissions in identified metro and rural catchments • Prospective recruitment • Informed consent and interview at convenient time • Suicide cases • Enumerated through Coronial data for identified metro and rural population catchments • ‘Next of kin’ contacted • Informed consent and third-person interview at convenient time • Controls • Random sample of census collection districts in study catchments (high % young adults, representive of SES dist.) • Door knocking to find an 18-34 year old. (Info. on coverage, participation rates etc. retain). • First person interview for AS • Third person interview for S (i.e. “can you nominate a relative or friend to do an interview about you”) • Sex and age-group matching

14. Ethical implications • Many. • and some that arose after funding and clearances were sought. But that is a story for later in the course... • Primary consideration relates to interviews of relatives of suicide cases and attempted suicide cases • potential distress and potential adverse events (e.g. pre-existing mental illness) • Detailed study information provided, informed consent • termination of interview at any time • period of at least 3 months since suicide for relatives • Clear referral pathways for those distressed • Safety protocols and debriefing for interviewers • Data confidentiality a big issue • De-identified • Automated data collection, password protected files • Project documentation, consent forms etc locked and only accessible to project staff

15. Analytic strategy • Analysis will commence with bi-variate tabulation of the relation between the outcome (completed or attempted suicide) and each of the risk factors separately. • tabulation undertaken separately for major age, sex, and demographic groups to produce proportions and unadjusted odds ratios which will be tested by Chi-square or exact tests if required • Specified hypotheses will be tested and sub-group analysis and interactions will be examined where appropriate. Multi-variable analysis will proceed via conditional logistic regression in which cases and controls are age and sex matched. This approach will permit the calculation of odds ratios of categorical variables or slopes of continuous variables, adjusted for other factors. • Sex-specific analyses will be required, although analysis of interaction terms between sex and other variables may suffice in some instances. Sub-group analyses specific to geographical area, and socio-economic status will be conducted • Aggregate data on social and economic characteristics of small area of residence to be analyzed as group-level factors simultaneously with individual factors using multi-level (hierarchical) modelling. • The data will also be compared to standardized sources of information such as the National Health Survey and the NSMHWB. This will provide corroborative evidence of validity of findings if similar prevalences are documented in alternative sources and contexts.

16. Bias and confounding • Selection bias • minimized because both cases and controls are population-based • Effect of refusal of cases or controls (or relatives) to take part, or inability to locate controls? • Use of administrative and clinical data from cases of attempted suicide who decline to participate to assess selection bias • For suicides whose relatives decline to participate coronial, postmortem, toxicological and death certificate data will be available • Sensitivity analyses will be performed to estimate the effect of plausible ranges of selection bias in cases and controls. • Measurement bias • differential recall bias? • minimised by design? (i.e. third person info. compared, also with first-person) • In-depth training of interviewers • Confounding • Age, sex, geographic area, and ethnicity will be controlled partly by strata matching of cases and controls on age and sex, and adjusted for by multivariate modelling where applicable • Not where involved in a (proposed) causal chain (i.e. intermediaries)

17. Timeframe and budget • Timeframe • Budget • for later in the course

18. Outcomes and significance • Internationally unique case-control study of suicide and attempted suicide by focussing on the ‘at risk’ age of Australian young adults. • Population based and have a sufficient number of subjects to conduct multivariate modelling of individual and socio-demographic variables, such as rurality and SES, hitherto not examined in a case-control context. • As a large case-control study of youth suicide this project will have international significance because the case numbers will permit detailed examination of inter-relationships between hypothesised predictor variables, occurring at individual and societal levels. • Innovative assessment of the extent of recall bias will also be undertaken. • Results of examination of the specific hypotheses should lead to more focussed approaches to suicide prevention according to urban-rural residence, socio-economic status, and perhaps ethnicity. This will be expected to inform suicide prevention efforts both through health services and in social and economic policy.