Can the salmon bias effect explain the migrant mortality advantage in England and Wales?
Wallace, M. & Kulu, H. (2018) CALLS Hub conference, University of St Andrews, UK, 23 March 2018 [ONS LS]
Despite researchers regularly observing a “migrant mortality advantage” in high-income destination countries, it remains unclear whether empirically observed low mortality among foreign-born relative to natives is genuine, or the result of censoring and selection biases inherent in the remigration of foreign- born people. Our aim is to determine whether the main mode of selection bias, the “salmon bias effect” (remigration triggered by poor health), can account for the migrant mortality advantage. We use the largest longitudinal resource in the United Kingdom, the Office for National Statistics Longitudinal Study, to fit discrete-time survival models and observe which foreign- born groups experience a migrant mortality advantage and/or salmon bias effect. For groups in which we observe both, we correct their mortality (using an indirect method) to see whether the salmon bias effect can explain the observed mortality advantage. Importantly, we demonstrate that for many foreign-born groups a mortality advantage exists in the absence of the salmon bias effect. Furthermore, in cases which we observe a migrant mortality advantage and a salmon bias effect (males and females from India, Pakistan and Bangladesh, and the Caribbean), the latter cannot sufficiently “explain away” the former. Taken together with previous findings on censoring bias in the United Kingdom and the wider international literature on censoring and selection biases, it becomes clear that biases arising from remigration cannot sufficiently explain the migrant mortality advantage.
Output from project: 0301579