The findings published in the December issue of the academic journal Demography challenge the common view that the cause of the poor health of Irish immigrants to England is that conditions in England were very stressful for the Irish-born migrants.

Rather this research shows that a large fraction of those who migrated to England throughout much of the 20th century suffered from recently well-documented physical and sexual abuse among Irish children born between 1920 and 1960. The study also suggests a new model of understanding immigration patterns in general around the world that accounts for the high physical and emotional costs often associated with staying in an individual's native country.

"Explanations about the struggles among Irish immigrants that rely exclusively on troubled assimilation may be missing a significant part of the story," said James P. Smith, the study's corresponding author and the Distinguished Chair in Labor Markets and Demographic Studies at the RAND Corporation, a nonprofit research organization. "Our findings suggest that emotional and physical experiences during childhood in Ireland appear to have spurred them to migrate and had a large influence on the future health of immigrants in England."

The study found that among people who stayed in Ireland and who were born between 1931 and 1960, about 10 percent reported being subjected to sexual or physical abuse. That contrasts to abuse reported by more than 15 percent of those who migrated from Ireland and then later returned to the nation.

Other authors of the study are Liam Delaney of University College Dublin and the University of Stirling and Alan Fernihough of University College Dublin, Ireland.

Historical interactions between Ireland and England underwent several shifts during the 20th century that changed incentives to migrate as well as the composition of those flows. While the United States was the primary destination for Irish immigrants in the 19th century, England was the primary destination during the 20th century.

During much of the 20th century, the Irish-born population in England generally has been in worse health than either the native population or the ethnic Irish population living in Ireland.

The trend ran contrary to the commonly observed phenomenon known as the "healthy migrant effect," where recent immigrants to industrialized nations are healthier than people in both the country they leave and their destination country. The explanation is that people who migrate generally tend to be younger and healthier than populations as a whole, even at the same age.

The researchers say the substantial Irish migrant health penalty is seen primarily among people born between 1920 and 1960. Irish immigrants to England who were born more recently are generally healthier than the native English population, a more-typical pattern that reflects the healthy immigrant effect.

The common view about the cause of the poor health of Irish immigrants to England is that conditions in England were very stressful for Irish-born migrants, particularly because of sporadic political violence that has occurred between the two countries.

To better understand and contrast the mental and physical health of Irish immigrants, the research team analyzed information from two large Health Surveys for England surveys that have tracked the health and behavior of people living in England who were born in Ireland and England. In addition, researchers used information from the Irish Longitudinal Study on Ageing and Living in Ireland (TILDA) data collected by researchers at Trinity College Dublin, which included data on childhood abuse of Irish return migrants from England.

Researchers also examined reports that documented widespread child abuse in Ireland. For example, the national Commission to Inquire into Child Abuse in Ireland investigated allegations of widespread abuse in a network of 60 Industrial and Reform Schools across Ireland, concluding that children sent to the institutions were frequently subjected to sexual and other forms of abuse.

Smith, Delaney and Fernihough document evidence that a large fraction of Irish children who were subjected to abuse appear to have migrated to England throughout the 20th century.

"The Irish who migrated to England were less educated and less healthy than their counterparts who remained in Ireland." said Delaney, professor of economics at Stirling University and a visiting professor at the University College Dublin-Geary Institute.

Researchers say their findings suggest a new way of considering the needs of migrants in many parts of the world, since many people suffer from persecution in their homelands because of their ethnicity or other attributes. Such migrants have very different outcomes and needs than the typical "economic" migrant.