Modelling changes in the determinants of PHI utilisation in Western Australia across five health care policy eras between 1981 and 2001.

Objective: In this study of the Western Australian population we analysed changes in the demographic determinants of PHI use across health policy eras. Specifically, we aimed to predict the probability that an individual, defined by a pre-determined set of characteristics, would utilise PHI for in-patient hospitalisation in WA in each of five health policy eras spanning 1981-2001.
Methods: The WA Data Linkage System was used to extract hospital morbidity data from 1 January 1981 to 31 December 2001. Random effects logistic regression analysis was used to estimate the likelihood of utilising private health insurance in each of five health policy eras based on the timing and composition of changes in federal health care policy.
Results: The use of PHI for in-patient hospitalisation fell significantly from 1981 to 1997 (61% above to 53% below the odds of being a public patient). From 1999, however, the odds of using PHI substantially increased to 16% above that of being a public patient. The likelihood of using PHI in all age fell approximately exponentially across successive health policy eras compared with that in the oldest (70+ years) age group. From 1997 onwards, the relative probabilities of average and disadvantaged individuals using PHI substantially increased compared with extremely advantaged individuals.
Conclusion: Our study found that the overall likelihood of utilising PHI versus utilising Medicare for in-patient hospitalisation, adjusted for all demographic characteristics, decreased between 1981 and 1998 but increased precipitously after 1999. We also found that the determinants of using PHI have changed significantly across health policy eras. The most significant changes occurred with respect to age (the probability of PHI use by older individuals increased) and socio-economic status (the probability of PHI use by average and disadvantaged individuals increased). This shift in the effects of determinants of PHI suggests that the introduction of the recent health policies were associated with a change in both the age and socio-economic profile of individuals who utilise PHI.