Inequalities in health are well documented. But it is less clear why inequalities between people and places change over time. One mechanism that may contribute is the redistribution of differently healthy people between locations, area types or social classes. 

Though the relationship between these highly inter-dependent mobility processes, the resulting socio-spatial trajectories, and health inequalities is widely explored, conclusions vary. This, in part, is due to the different approaches employed. 

For example, modelling individual-level outcomes – a common approach – reveals the relationship between particular socio-spatial trajectories and health outcomes. Yet it does not reveal the influence on health inequalities at the population level. There may be a strong implication that differences between groups may affect either area or class relationships, but this is not specifically measured. 

A more appropriate framework of analysis must establish three key questions to determine the relationship between socio-spatial trajectories and changing health inequalities. Specifically:

• To what extent do health gradients vary when populations are able to move between area types or social classes compared to those arising when populations are put back into their area type or social class of origin? 
• To what extent does the health status of those entering the most and least advantaged areas, or highest and lowest social classes differ from those leaving these areas or classes?

And finally, given the inter-relationships between opportunities for migration or residential mobility and social mobility,

• To what extent does the patterning to health by transitions into and out of differently deprived areas or social classes vary migrant status? 

Using data from the Office for National Statistics Longitudinal Study, we demonstrate three methods that collectively reveal whether and how different socio-spatial trajectories can contribute to changing health inequalities at the population level. Our framework offers insights into the nature and extent of inequalities within population, identifying mechanisms that can contribute to changing inequalities while also illustrating differences in opportunities for and nature of social or geographic mobility. 

Future work, in combination with this framework, must examine the complex interplay between people, places and politics to better unpack the injustices in uneven opportunities for social or geographic mobility, particularly where this contributes to widening health inequalities. 

To learn more, see our open access paper published by Population, Space and Place: ‘Establishing a framework of analysis for selective sorting and changing health gradients’, Frances Darlington-Pollock and Paul Norman https://doi.org/10.1002/psp.2359