Migration levels are increasing as our world continues to become more connected. In Australia, migrants comprise almost 30% of the total population . Migrants are a heterogenous group. There are economic migrants and those who migrate for humanitarian reasons . Humanitarian migrants may have experienced traumatic or dangerous events which have the potential to cause a range of health issues, both physical and mental. The United Nation’s (UN) 2030 Sustainable Development Goals (SDGs) highlight the importance migration plays in sustainable development, with over half the goals relevant to migrant wellbeing .
Migration can provide many benefits. In Australia, managed labour migration plays an important role in creating a flexible labour market . In the UK, migrants provide a solution to staff shortages . Economic migrants on average contribute more through taxes than they cost a host country . Migration can impact on the demographic composition of the host and source countries. Migration can contribute to addressing the aging population problem in high income countries. For source countries, remittance payments can promote economic development, but it may also cause brain drain which will have negative economic consequences .
Migration is a politically emotive topic. There is a common misconception that migration can put a strain on public services. The impact of migrants on public expenditure is dependent upon the assumptions of the model used and how migrants are defined. As migrants are such a heterogenous group, one cannot make conclusions a priori what the impact of migrants will be on the health system. The ‘Healthy Migrant Effect’ [7, 8] predicts that because migrants tend to be younger, fitter, and healthier than the host population. Thus, on average they will require fewer health care resources. To qualify as an economic migrant, in some countries such as Australia, there are health and age criterion for entry . In further support of the concept that on average migrants are healthier is the ‘Salmon Bias theory.’ This suggests migrants return to their country of origin in later life or in poor health . Thus, their impact on the health care system of the host country will be minimal. Conversely, there is the convergence theory which suggests that migrant’s health and lifestyle tend to converge to that of the host population because of acculturation . This would suggest that migrants in the long term would have similar service usage to the host population
The evidence supporting the above theories is mixed. This could be because of differences in how countries classify migrants . For example, nationality, country of birth, and citizenship are all used to classify migrants . Cheswick et al.  found for Australia that the self-reported health of economic migrants converged to the mean for native Australians, but the health of humanitarian migrants remained poor. These findings suggest that how migrants are defined is important for understanding their health and what this means for their use and need of health services.
It is cost-effective that migrants can access healthcare on demand. There is evidence suggesting that costs of healthcare increased when asylum seekers and refugees were initially unable to access treatments, in comparison to when healthcare was not restricted . A systematic review of health service usage amongst migrants and host populations across several European countries identified various inequalities . Emergency care was utilised more by migrants. However, outpatient departments recorded a lower use by migrants. This suggests there could be barriers which prevent migrants from accessing non-emergency medical care such as routine check-ups or preventative screenings. Another study analysing data from several European countries highlighted treating migrant populations’ health issues promptly, out of hospital, is more economically effective than waiting until hospitalisation is required .
A gap in public health research on migrant health and their health service usage in Australia has been identified . Additionally, there is a lack of evidence, looking at health service usage across the life course and across different migrant groups. Understanding this heterogeneity across the life course as well as across migrant groups is important for the cost-effective targeting of services to those most in need. Differences in primary and secondary service usage by migrant groups can provide clear evidence on which groups may have difficulty in accessing services.
We explored differences in primary and secondary care across migrants from different regions across the life course. Next, we identified how differences in observed characteristics and unobserved barriers in access such as cultural factors, inequities in access to services, or differences in quality of education for example, may explain any of the differences between migrant groups and the host population primary service usage . We solely focus on differences in primary care as higher service usage of secondary care by migrant groups may reflect barriers to access for preventative/ basic care. We hypothesise that younger economic migrants are likely to be healthier or have a similar level of health to the host population. Younger Humanitarian migrants are more likely to have worse health compared to the host population . However, if there are barriers to accessing services then primary service usage may be lower for this group and secondary service usage will be higher. The composition of the migrant population (humanitarian or economic) will determine what the overall association will be for each region. For older migrants, we hypothesise that if they have had to engage in low skilled manual work throughout their adult life and have faced barriers to health care services as younger adults, they are likely to be in worse health than the host population. This may mean that older migrants use both more primary and secondary services. Conversely, depending on the nature of barriers to services, after being in Australia for a number of years because of acculturation these barriers may have decreased if migrants better understand the health care system. Acculturation would suggest that service usage for older migrants was similar to that of the host population. Overall, our results can be used to help plan the provision of health care resources for all to maximise health, reduce health care costs, and minimise health inequalities.