This study is unique among studies of migration and risk for psychiatric disorders in the use of cross-national data to compare morbidity in a representative sample of migrants with that in their source population. Respondents on both sides of the border were interviewed within the same time frame using the same diagnostic interview. While our early pilot study included only a small sample of English-speaking migrants, this study includes a larger sample of migrants interviewed in their choice of English or Spanish. In addition, the comparison group in this study, members of families in Mexico with a migrant in the US, provides a robust adjustment for migrant selection. The finding that migrants are at higher risk for onset of depressive and anxiety disorders during the years following migration, compared with family members of migrants who remained in Mexico, provides the first direct evidence that experiences as a migrant might lead to the onset of clinically significant mental health problems in this population. In particular, migrants were at higher risk of depressive disorders, inclusive of major depression and dysthymia, as well as GAD and social phobia. In addition, when the relatively small increase in risk across the entire immigrant population (OR=1.4) is broken down by birth cohorts, a much larger effect is revealed among a restricted segment of the population, those in the most recent birth cohorts, with the strongest association found in the youngest cohort, those age 18 to 25(OR=3.9).
This evidence is particularly important because the two findings from previous studies that have been cited as evidence of an adverse effect of migration on mental health are open to alternative explanations. First, previous studies reported associations between poor mental health and acculturation, i.e. the extent to which immigrants or members of ethnic minority populations have adopted behaviors typical of mainstream Americans or gained proficiency in English, when both are assessed contemporaneously 6, 29
. This association is purported to reflect, in part, the impact of negative experiences faced by immigrants in the process of assimilation, i.e. acculturative stressors. However, these findings can be explained by high levels of risk for psychiatric disorder among the US-born members of ethnic minority populations, who have both high risk for psychiatric disorders and high levels of acculturation relative to immigrants 9, 30
Second, previous studies have found that immigrants who have lived in the US for longer periods of time have higher risk for psychiatric disorder than immigrants who have recently arrived8
. That finding seems to indicate that a longer period of exposure to the US leads to a decline in mental health. However, the association between duration of residence and onset of disorder is confounded by age at migration: holding age constant, immigrants who have lived in the US longer migrated at younger ages. Recent studies have found that immigrants who arrive in the US before age 13, have a much higher risk for mood and anxiety disorders than immigrants who arrive in the US as adolescents or adults31
. The apparent effect of longer duration of residence in the US may reflect the high levels of risk among immigrants who arrived as children, who, compared with other immigrants of the same age, are likely to have lived in the US for longer periods of time. The difference might be in age at migration rather than duration of residence in the US.
This study provides evidence of an adverse effect of migration on mental health among Mexican migrants to the US that overcomes important limitations of previous studies of this population. First, the sample is limited to first generation immigrants, to distinguish mental health problems among immigrants from mental health problems of US-born offspring of immigrants. This sample offers more direct evidence on the mental health effects of experiences in the years following migration to the US. Second, the use of survival models ensures that disorders which occurred prior to migration were not counted as potential effects of migration. Third, we improve the adjustment for migrant selection by comparing migrants in the US with a sample of family members of migrants in Mexico. The use of family members of migrants as a comparison group adjusts for between-family migrant selection
, i.e. differences between Mexican families with and without migrants that might influence the risk for depressive and anxiety disorders. Sociological research suggests that family characteristics, such as economic security, which enables the initial investment required for migration, are important determinants of migration 32–34
A remaining limitation of this study is the possibility of residual confounding (of the effect of migration on mental health) by pre-migration differences between migrants and non-migrants. Our pilot study suggested that there is negative health selection in this population, i.e. that indicators of risk for psychiatric disorder are associated with higher likelihood of migration11
. Confounding might occur at the family level, i.e. by differences between families with and without migrants, or at the individual level, i.e. by differences between migrants and non-migrants within families. Restriction of the control group to non-migrant members of families of migrants in Mexico is intended to account for confounding at the family level. Differences between migrants and non-migrants within families were accounted for in this study by treating the exposure, migration, as a time-varying covariate; disorders that preceded migration, including those occurring in the year of migration, were counted towards the baseline risk among non-migrants. In addition, estimates were adjusted for prior onsets of comorbid psychiatric disorders, which might have occurred before or after migration. Nonetheless, the possibility of residual confounding cannot be entirely ruled out. In supplementary analyses of this sub-sample, conducted to address the question of migrant selection, migration remained associated with higher risk for onset of depressive and anxiety disorders after adjustment for childhood adversity profiles.
Reliance on recall of the lifetime occurrence of psychiatric disorders is also a potential limitation of this study35
. Inaccuracy in recall would bias the results if migrants were more likely to recall past symptoms than family members who remained in Mexico. The potential influence of recall bias should be considered in light of the observed inter-cohort variation in the association between migration and risk for disorder. We would expect recall bias to be more severe in older cohorts, because they have a longer period of time over which they are asked to recall their experience of psychiatric symptoms. However, in this study the association between migration and disorder was strongest in the youngest respondents, among whom the influence of recall bias is likely to be minimized.
Finally, the differences observed here may also reflect differences in idiom of distress between migrants and their families of origin. These differences are minimized in this study by the use of the same fully structured diagnostic interview, which assesses specific symptoms rather than general complaints, and by the shared Mexican cultural background of the entire sample. Future studies of shifts in idiom of distress among migrants might further test whether the apparent impact of migration on mental health can be accounted for by methodological difficulties in assessing psychiatric disorders cross-culturally.
This study advances our knowledge of the transition in population levels of risk for depressive and anxiety disorders from the relatively low prevalence found in Mexico13
to the relatively high prevalence found in the Mexican origin population of the US36
. Evidence now suggests three distinct components of this transition. First, there is evidence of negative mental health selection, i.e. that individuals who migrate have less favorable childhood mental health profiles than individuals who do not migrate 37
. Second, evidence from this study suggests that after arrival in the US migrants are at still higher risk than Mexicans who did not migrate, even after accounting for selection factors. Third, Mexican-origin individuals, whether born in Mexico or the US, who spend their childhood in the US are at roughly equally high levels of lifetime risk as the general US-born population31
Identifying these components of the transition in risk for psychiatric disorder associated with migration may help identify and test suspected etiological factors. Studies of migration and mental health have focused attention on discrimination as one likely cause of increased risk for psychiatric disorder. Studies of Caribbean-origin migrants in Europe suggest associations between discrimination and psychotic disorders 38,39
. In the US there is evidence of an association between experiences of discrimination and depression among Hispanics 40, 41
. While suggestive, current evidence is limited to studies that compare migrants with descendants of immigrants born in the host country. In addition, associations between migration and mental health may not be generalizable across migrant groups, which differ dramatically in the factors influencing migration and the conditions in the receiving host country.
Potential explanations for the inter-cohort variation in the effect of migration might lay either in change in the composition of migrants across birth cohorts or in changes in the social context of immigrant absorption in the US. Historical studies of migration from Mexico to the US have found that the demographic composition of the migrant population has been relatively stable over the periods covered in this study42
. Therefore it is unlikely that secular changes in the types of migrants account for the observed variation in the effect of migration. Changes in the context of immigrant absorption in the US have also occurred in this period that would likely affect the experience of recent birth cohorts, most notably the immigration reforms of 1965 and 1986. The finding that elevation in risk for depressive and anxiety disorders occurs among recent birth cohorts of Mexican migrants may help guide future research by locating the effect of migration within the particular experiences of this sub-population.