Mortality differentials 1991−2005 by self-reported

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Mortality differentials 19912005 by self-reportedethnicity: ndings from the ONS Longitudinal Study

Anne P Scott,1 Ian M Timus2

1London, UK2Department of PopulationHealth, London School ofHygiene & Tropical Medicine,London, UK

Correspondence toProfessor Ian M Timus,Department of PopulationHealth, London School ofHygiene & Tropical Medicine,Keppel Street, London WC1E7HT, UK,[email protected]

Received 11 December 2012Revised 15 April 2013

Accepted 2 May 2013

To cite:Scott AP,Timus IM.J EpidemiolCommunity HealthPublishedOnline First: [please includeDay Month Year]

doi:10.1136/jech-2012-202265

ABSTRACTBackground Research on ethnic differentials inmortality in England and Wales has focused onimmigrants because, until now, studies collecting dataon ethnicity have not covered sufcient deaths toinvestigate the subject. International migrants areselected for good health and tend to have low mortality.Methods We investigated all-cause mortality at ages179 in 19912005 by self-reported ethnicity andcountry of birth. The data are from the Ofce forNational Statistics Longitudinal Study of England andWales for the cohort aged 064 in 1991 (n=436 195).Poisson regression was used to adjust the estimates formetropolitan residence and three indicators of

socioeconomic status.Results White, Black Caribbean, Other Asian andOther immigrants all had lower mortality than Whitesborn in the UK. Indian, Pakistani, Bangladeshi andChinese immigrants had lower mortality than the UK-born Whites living in similar circumstances to them. Bycontrast, the UK-born Black Caribbean group had highermortality (RR=1.38, 95% CI 1.03 to 1.86) than theUK-born Whites. This excess mortality was accounted forby their low socioeconomic status. Within the BlackCaribbean population, the UK-born individuals hadsignicantly higher mortality than those born abroadwhether or not the estimates were adjusted for

socioeconomic status and metropolitan residence.Adjusting exposure time for undocumented emigrationmade little difference to the estimates.Conclusions Immigrants are selected for good health.This has offset the impact of socioeconomicdisadvantage on the mortality of minority ethnic groups.As the immigrant population ages and the UK-bornminority ethnic population grows, ethnic differentials inall-cause mortality are likely to change.

INTRODUCTIONResearch into the mortality of minority ethnic popu-lations in England and Wales is limited because noinformation on ethnicity is collected on death certi-cates.1 Until 1991, no information on ethnicitywas available from the Census either. Moreover,because minority ethnic groups are both a small pro-portion of the entire population and relativelyyoung, most sample-based inquiries cover too fewdeaths to study ethnic differentials in mortality.

Several earlier studies have investigated mortalityby country of birth.27 A cross-sectional analysis for20012003 found that all-cause mortality is oftenlower among adults born abroad than for the popu-lation born in England and Wales. For example,

this was true for men born in India and China andHong Kong, and women born in the West Indies,

West Africa and China and Hong Kong.

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One explan-ation of such ndings is that international migrantsare selected for good health.2 8 This is often termedthe healthy migrant effect. Moreover, returnmigrants may be selected for poor healththesalmon bias.1 9 10 In addition, the mortality of differ-ent ethnic groups has been estimated from 2001Census data on limiting long-term illness.11 Theseestimates suggest that most minority ethnic groupsexcept the Chinese have higher mortality than theWhite population, with the Pakistani and Bangladeshigroups doing particularly badly.

This paper describes variations in mortality inEngland and Wales in 19912005 by self-reported

ethnicity and country of birth using data from theOfce for National Statistics (ONS) LongitudinalStudy (LS). It distinguishes the mortality of theimmigrants from that of the UK-born individualsfor each ethnic group, investigates what part of thedifferences in mortality according to birthplace andethnicity is accounted for by commonly used indi-cators of socioeconomic status (SES), and assessesthe impact of unobserved embarkations on esti-mates of mortality for minority ethnic groups. Wehypothesise that while rst-generation immigrantsare a select group with low mortality, their off-spring will have higher mortality than the White

UK-born majority because of their relatively lowsocioeconomic position.

METHODSONS Longitudinal StudyThe longitudinal study (LS) is a database that linkscensus and vital events records from 1971 onwardsfor 1% of the population of England and Wales.12

We studied the cohort of LS members traced in theNational Health Service Central Register before orduring 1991 Census processing who were aged


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Statistics Socioeconomic Classication.1417 All members of afamily were assigned to the highest status parental occupation.17

The analyses also took into account where people lived in 1991,distinguishing inner and outer London from other metropolitanareas and non-metropolitan areas.

In addition to calculating descriptive statistics, we modelled therelative risk of dying according to various sets of characteristics bymeans of Poisson log-linear regression models for rates withperson-years spent in the LS as the offset variable. All the estimatesof mortality presented have been adjusted for 5-year age group,

sex and date of exposure (1991

1998 or 1999

2005). We alsomodelled the data using negative binomial models but found noevidence of overdispersion (results not shown).

Exit from the LS occurs when individuals die or notify theirdoctor or Health Authority (HA)subsequently Primary CareOrganisationthat they are emigrating. An emigrant can re-enterthe LS by reregistering with an HA. The calculation of the person-years that the cohort spent exposed to the risk took into accountexits and re-entries. It also made allowance for undocumentedemigration. In particular, using an algorithm developed for mortal-ity research using the LS, it was inferred that individuals had emi-grated if their HA cancelled their registration because they had notbeen in contact with their doctor for several years and they thenfailed to reregister with a doctor within a year. A full account ofthis algorithm is available elsewhere.18

Some additional undocumented emigrants will exist amongthe LS members who could not be accounted for at the 2001Census despite not being known to have emigrated or died.These missed emigrants bias the death rates downwards byinating their denominators. To assess the potential impact ofthis, the key analysis is presented incorporating an adjustmentfor it, as well as with denominators adjusted only for reportedembarkations and those inferred from HA deregistrations.Because it addresses the issue of unreported censoring by emi-gration, not unreported events, our approach differs from stand-ard methods for addressing attrition and wave non-response inpanel studies.1922

The adjustment used logistic regression to model how muchof the period between the 1991 Census and end of 2005 LS

members who were either recorded as emigrating or identiedin the 2001 Census spent outside the country as a function oftheir 1991 characteristics: age, sex, place of residence, SES mea-sured by all the three indicators we consider, ethnicity interactedwith whether they were migrants and the length of residence inthe UK of immigrants. This model was then used to predict howmuch of each 7-year period under study the 10% of the cohortwith no information after 1991 spent as emigrants. If the prob-ability of undocumented embarkation was random conditionalon the 1991 characteristics used to model it, this procedure

will eliminate bias due to unrecorded loss to follow-up betweenthe 1991 and 2001 Censuses.23 Because no way yet exists ofestimating undocumented emigration in 20012005, no adjust-ment was made for it.

RESULTSTable 1 presents basic descriptive information on the cohort. Ofthe LS sample aged 92% described themselves asWhite. The largest minority ethnic groups were Indians, Pakistanisand those of Black Caribbean origin. About two-fths of allnon-White people were born in the UK, compared with only aboutone quarter of Bangladeshis, Chinese and Other Asians. Only 4%of the White cohort members were born abroad.

The age structure of the different ethnic groups varied. Likethe distributions by place of birth, this reects differences in fer-tility and in the dates and ages at arrival of immigrants. TheBlack African, Other Black, Pakistani and Bangladeshi groupswere least likely to be aged 65+. The White and BlackCaribbean groups contained more older people than any of theother ethnic groups. Even so, the UK-born Black Caribbeangroup only had a mean age of


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similar. The UK-born minority ethnic population was no morelikely than Whites to have reported their departure, but almostthree times more likely to have been deregistered. Individualsborn abroad were over three times more likely to have leftEngland and Wales than the UK-born, with emigrants identiedfrom deregistrations greatly outnumbering reported embarka-tions. These gures, and the differentials between the differentminority ethnic groups, emphasise the importance of taking HA

deregistrations into account in this analysis.The nal two columns of table 2 show the estimated propor-

tion of the follow-up period for which individuals not identiedin the 2001 Census and not known to have died or emigratedwere not at risk of dying in the UK because they had emigratedbefore 2001. On average, this group spent 6.9% of the periodof follow-up as emigrants, compared with 2.7% for those whocould be accounted for. However,


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Table 3 Per cent distribution in the 1991 Census of Longitudinal Study members aged


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in non-metropolitan England and Wales, but lower in outerLondon than elsewhere in the country.

Table 5 presents estimates of the coefcients of three models.The rst model examines how country of birth and ethnicitytogether affect mortality relative to the UK-born White popula-tion. The immigrants among the Black Caribbean and Other

groups accounted for their signicantly lower mortality than theUK-born White population. Whites born abroad also had lowermortality than Whites born in the UK. Focusing on theUK-born, the only minority ethnic group with signicantly dif-ferent mortality from Whites was the Black Caribbean popula-tion, which had 38% higher mortality (95% CI 3% to 86%).

The second model examines the net impact on mortality ofethnicity and country of birth adjusted for the impact of otherfactors. After controlling for all three measures of SES and placeof residence, no signicant ethnic differentials existed in mortal-ity among the UK-born population. In particular, the excessmortality of the Black Caribbean population born in the UKwas accounted for largely by socioeconomic disadvantage.

The third model contains the same explanatory variables, butreduces the person-years of observation to allow for undocu-mented embarkations of members of the cohort who are notknown to have died or emigrated but could not be identied inthe 2001 Census. This adjustment makes very little difference tothe relative risks of dying of the different ethnic groupsalthough, as expected, it slightly raises the mortality of someminority groups relative to the White UK-born population.

DISCUSSIONEthnic differentials in mortality remain difcult to investigatebecause ethnicity is not collected on death certicates inEngland and Wales, although it has been asked about on a vol-untary basis in Scotland since 2012.24 The LS provides such

information for England and Wales by linking the certicates tocensus records but only covers 1% of the population. Our

study beneted from being based on several more years offollow-up since 1991 than previous research using the LS,during which period minority ethnic populations continued togrow and age.1 Nevertheless, the sample of minority ethnicdeaths remained rather small for the study of this topic.

Unrecorded emigration of LS members who were not identi-

ed in the 2001 Census, but are not known to have died or emi-grated, was estimated by assuming that all embarkations in therest of the cohort had been identied and that individuals pro-pensity to migrate depends solely on their characteristics in1991 as measured here. No adjustment was made for undocu-mented emigration during 20012005. Equally, some peoplewhom we classied as emigrants because they were no longerregistered with a general practitioner will have remained in thecountry.25 People with no linked records subsequent to 1991were estimated to be 2.6 times more likely to emigrate by 2001than the rest of the cohort. Nevertheless, adjusting the exposuretime of this group downwards affected the estimates of differen-tial mortality only slightly because most of them did not emi-grate and they comprised only 10% of the surviving cohort.Given the insensitivity of our results to the adjustment made forundocumented emigration, bias from this source is unlikely tohave inuenced the conclusions reached by this study.

Distinguishing immigrant and UK-born members of minorityethnic groups revealed that the Black Caribbean populationborn abroad had lower mortality in 19912005 than Whitesborn in the UK despite their lower SES in 1991. This result isconsistent with the idea that migrants are selected for health. Bycontrast, the UK-born Black Caribbean population had highermortality than Whites born in the UK. However, the 88%of the Other Black group that were UK-born included manypeople who were wholly or partly of Caribbean descent butdescribed as Black British in the 1991 Census. They did not

share the high mortality of those reported explicitly to be ofBlack Caribbean descent.

Table 4 Relative risks of dying at ages 179 in 19912005 by place of birth, ethnic group, socioeconomic characteristics and area ofresidence, each adjusted only for age, sex and period of death, of Longitudinal Study members aged


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The excess mortality of the UK-born individuals who werereported to be of Black Caribbean descent is almost entirelyaccounted for by the indicators of SES included in the analysis.In other words, this group has relatively high mortality becauseit tends to be disadvantaged. Within the Black Caribbean popu-lation, individuals born in the UK have signicantly higher mor-tality than immigrants. This differential is not accounted for bydifferences in their SES.

The regression model that adjusted for SES and residenceshowed that, in addition to Black Caribbean immigrants,

Indian, Pakistani, Bangladeshi, Chinese, Other Asian and Otherimmigrants all had lower mortality than UK-born Whites whowere living in similar circumstances to them. This advantage isonly manifest in the unadjusted estimates for the Other Asianand Other groups. This suggests that immigrants from the Indiansubcontinent and China are also selected for health, but that theimpact of this on mortality has been offset by their social disad-vantages compared with the UK-born White population.

Our

ndings refer to the population in private householdsenumerated at the 1991 Census and are based on self-reported

Table 5 Relative risks (RR) of dying at ages 179 in 19912005 by place of birth and ethnic group of Longitudinal Study members aged


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ethnicity as coded then. The UK-born White population as iden-tied in 1991 is itself ethnically diverse including, for example,the children of Irish parents and those of Romani extraction.Some of these hidden minority ethnic groups may have highmortality. Substantial immigration has occurred since 1991 andthe results do not reect the mortality of this part of the immi-grant population. We also only examined the mortality of thoseaged


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Data sharing statement It is the policy of the Ofce for National Statistics thatthe LS should be available as readily as is consistent with maintaining thecondentiality of the data. Potential academic users working or studying in the UKHigher Education sector can access the data through the CeLSIUS programme.

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Mortality differentials 1991−2005 by self-reported