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Novel approaches to understanding risk
O1-2.5 Fallibility in estimating indirect effects: misclassification of the mediator matters more than collider bias
  1. T Blakley,
  2. K Carter,
  3. S McKenzie
  1. University of Otago, Wellington, New Zealand


Introduction Smoking is the largest single cause of preventable mortality and morbidity in Australia and many countries globally. The limited existing evidence suggests that smokers user fewer general practitioner (GP) services, but more hospital services, than non-smokers, and may not be benefitting from secondary prevention. We investigated use of GP services by Australians aged 45 years and over according to smoking status.

Methods Analysis of self-reported questionnaire data from 96, 522 participants in a population-based cohort study (the 45 and up Study), linked with data for national health insurance (Medicare) benefit payments and out-of-pocket-costs (OOPC). Generalised linear models were used to explore the relationships between smoking status, benefits paid and OOPC incurred. RRs were adjusted for age, sex, rurality, income, education, bodyweight, self-rated health, functional status and chronic conditions.

Results Current smokers were much less likely than non-smokers to be in the top cost decile for either benefits (RR 0.76, 95% CI 0.69 to 0.84) or OOPC (RR 0.61, 95% CI 0.55 to 0.68). Smokers used fewer preventive GP services (health checks, screening).

Conclusion Data linkage allowed complete capture of GP service use for a large population-based sample. After adjusting for a wide variety of access- and need-related factors, we found that Australian smokers are less likely than non-smokers to incur high costs for GP services. This held both for services provided for free, and those paid for by patients. Smokers may seek care less actively, perhaps because they are less health-conscious, or perhaps because they are avoiding censure from health professionals.

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