New Paper – Low immigrant mortality in England and Wales: a data artefact?

Guest Post by Matthew Wallace


Last week, I published a paper in Social Science & Medicine examining mortality among the major immigrant groups in England and Wales over a thirty year period from 1971 to 2001. While recent national media focus has fixated firmly on the fiscal cost of ‘health tourism’ – Migrants to face emergency NHS charges” (BBC), End of free NHS care for migrants under new bill” (Telegraph), Tough rules to stop health tourists” (Daily Mail) – there has been little focus on the health of immigrants who actually live in England and Wales. The health and mortality of these groups is of substantial interest to policy-makers. Evidence suggests inequalities in health by ethnicity and country of birth, but there has been insufficient consideration of the importance of country of origin and length of residence in the United Kingdom.

In short, results from the paper show low mortality (compared to non-migrants in England and Wales) for individuals from India, Pakistan, Bangladesh, Western Europe, China and group Other Asia. Analysis also shows that this low mortality begins converging to native levels over time – though low mortality persists for some groups at old ages. As to why we see these patterns, low mortality among first-generation immigrants provides evidence of a ‘healthy migrant effect’ whereby individuals initially ‘select’ for good health and the personality traits often associated with a successful migration (ambition, social adeptness and risk-resilience). This good health and low mortality then wears off over time as individuals ‘acculturate’ or adopt the unfavourable habits and behaviours of the host society.

There are of course many additional dimensions to the research which I do not cover here. If you would like to read the discussion in full, the paper is available online through journal Social Science & Medicine or alternatively, at: If there is anything you would like to discuss, please feel free to email me at The paper was co-authored with Dr Hill Kulu; the research was supported by the Economic and Social Research Council [ES/J500094/1] with permission from the Office for National Statistics. The next step of my research is to study the mortality of second generation migrants in England and Wales. Previous research suggests that this group do not share the low mortality of their parents and may actually have a higher mortality risk than natives.

Problems with percentages in population studies

Local coefficient of determination for log-ratio variables

Post by Dr Chris Lloyd

In conjunction with Vera Pawlowsky-Glahn and Juan José Egozcue, two internationally-renowned researchers in compositional data analysis (CODA), I have just published a paper in Annals of the Association of American Geographers (one of the top ranking geographical journals in the world), which shows why percentages cannot be properly analysed with standard statistical methods. Percentages are common in the spatial sciences, but it is not often realised that there are restrictions on how they can be analysed. An obvious example is a regression of one percentage against another  –  in this case the fitted model may predict values which are smaller than 0 or are larger than 100.

Percentages and proportions are referred to as compositional data and complete compositions typically sum to 100 (the case for percentages) or one (proportions). The AAAG article focuses on population studies and, using the example of religion in Northern Ireland in 2001, it shows how population data can be transformed into log-ratios; these new data can then be analysed using standard statistical approaches. The case study gives insights into how the population of Northern Ireland is distributed by religion and it shows that the most obvious geographical pattern relates to the ratio of Catholics to Protestants, although there are also distinct relationships between Catholics and individual Protestant denominations. Whether you are a Physical or Human Geographer, or indeed from an entirely different discipline, percentages or proportions should be used with caution and I hope that this paper helps some researchers make more informed choices.