QMSS2 Immigration & Population Dynamics: Summer School PROJECTION METHODS FOR ETHNICITY AND IMMIGRATION STATUS The e

1. QMSS2 Immigration & Population Dynamics: Summer School PROJECTION METHODS FOR ETHNICITY AND IMMIGRATION STATUS The estimation of ethnic fertility Paul Norman School of Geography University of Leeds • Acknowledgements • ESRC, ONS, GROS, NISRA, OS, UKBORDERS, CDU

2. Projections by ethnic groups … why? • Applied reasons • Age-sex estimates by sub-groups needed • Ethnic group numbers for equal opportunities, education support, health • Output quality reasons • If sub-groups ‘behave’ differently, the quality of the whole will be improved • Fertility differentials? • Ethnic group fertility variations • Cultural differences on family size, age having children, etc • Other sub-group differentials? • Anything discussed here ‘could’ be achieved for other groups • Tenure, educational achievement, social class

3. Measuring fertility: all women • Fertility rates • Age-Specific Fertility Rates (ASFRs) (= births / women * 1,000 for each age(-group)) • Total Fertility Rates (TFRs) (= sum of ASFRs / 1,000 * age interval)

4. a.) TFR = 1.69 b.) TFR = 1.44 Fertility rates in a projection • Projections use ASFRs: applied to women of child-bearing age • May be applied before other demographic components • May be applied after survival and migration components a.) 9,788 babies = 5,013 boys & 4,774 girls b.) 7,927 babies = 4,060 boys & 3,867 girls

5. a.) TFR = 1.69 b.) TFR = 1.44 Age-specific variation • Age-specific information necessary • Shape of curve affects speed at which population ‘replaces’ itself • Intergenerational effects N.B. Can have same TFR for different shape of curve TFR ‘just’ a summary measure

6. Age-specific variation • Age-specific information necessary • Trends in shape of curve useful in a projection Year TFR 1981 1.79 1986 1.77 1991 1.83 2001 1.74 2006 1.85

7. Subnational variations in fertility Geography needed Bradford Leeds Year TFR 1981 2.20 1991 2.14 2001 2.17 2006 2.33 Year TFR 1981 1.72 1991 1.74 2001 1.44 2006 1.58

8. Fertility rates: data sources … • National & subnational geographies within the UK • Vital Registration system: births by age of mother • National > local authority (LA) but subnational data restricted to 5 year age-groups • Census or mid-year estimates provide populations at risk • ASFRs & TFRs possible • Births counts: > wards (sub-LA geography) • ASFRs & TFRs not (conventionally) possible • Fertility rates: data by ethnic group … • National & subnational geographies within the UK • Vital Registration system: does not collect data by ethnic group (but does have country of birth of mother, though not useful for second generation immigrants) • Need to use proxy indicators and estimate fertility

9. Fertility indicators by ethnic group … • Vital Statistics Geography: national to local • Age: five year detail • Populations • Geography: national to local • Age: five year detail • Ethnicity: up to 16 groups (2001) • Survey • Geography: national (& region) • Age: (SYA &) five year detail • Ethnicity: (15,) 8 & 4 groups (2001)

10. Fertility indicators by ethnic group … • Age-specific variation (at national level) • Survey microdata (annual) • Child : Woman Ratios (CWR) by ethnic group (fair detail) • Presence of child per woman by age and ethnic group (broad) • Proportions, Statistical model, Mathematical function • Geographical variation (at LA level) • Proxy indicator of family size by ethnic group • Child : Woman Ratios used alongside TFRs for all women • Source UK Census aggregate data (decennial) • ‘Triangulate’ to produce local estimates • Vital Statistics with Geographical and Age-Specific information

11. Age-specific variation in ethnic fertility • National level age-specific fertility information • Data source: a national coverage microdata survey • Labour Force Survey (LFS) • Whilst original focus is ‘labour’ … has variables on • Age, sex & ethnic group • Household structure & relationships • Presence of dependant children • But … large sample but small numbers so grouped age and grouped broad ethnicities • Study population • Women aged 15 to 44 by ethnic group (using five year age-groups), who are not (as far as it is possible to tell) • The sister, grandmother; or • Otherwise not the mother of a child in the family or household

12. Age-specific variation in ethnic fertility • Crosstabs … • Presence of dependant child by ethnic group • Child : Woman Ratios (CWRs) are an indicator of family size • Child aged 0-4 / Women aged 15-44 • TFR(e) = TFR(aw) * ( CWR(e) / CWR(aw) ) • Where: e = Ethnic group & aw = All women

13. Age-specific variation in ethnic fertility • Simple crosstabs … • Presence of dependant child by age of mother & ethnic group • Age-specific rates spiky (even with broader groups)

14. Age-specific variation in ethnic fertility • Statistical model • Logistic regression • Binary outcome: Presence / Absence dependant child • Explanatory variables ethnic group & age-group • More practical are separate models for each ethnic group • Model coefficients: log odds converted to probabilities

15. Age-specific variation in ethnic fertility • Mathematical function • To smooth spiky rates (& provide single year of age information) • Hadwiger curve • … input 5 year rates … SPSS syntax: • model program B=4 C=28 a=1 . • compute White_Pr = (a*b/c)*(c/age)**(3/2)*exp(-b*b*(c/age+age/c-2)) . • NLR White …

16. Age-specific variation in ethnic fertility • Using the estimated ASFR curves: whether derived from statistical model or Hadwiger function … • Use proportional difference to ‘All Women’ curve to scale the VS-derived ASFRs • e.g. ASFR(sa) = ASFR(aw) * Pr(sa) / Pr(aw)

17. Age-specific variation in ethnic fertility • Use TFRs from CWRs to scale the curves for overall level & to add ethnic detail

18. Age-specific variation in ethnic fertility • Calculate numbers of births Scale births

19. Age-specific variation in ethnic fertility • Recalculate ASFRs • Consider iterating to improve the ‘fit’ • A set of ‘plausible’ & ‘robust’ national level ASFRs by ethnic group now produced • Now need to think about subnational variation …

20. Geographic variation fertility • For each location (Local Authority) … • Age-Specific Fertility Rates and Total Fertility Rates • Vital Registration system: births by age of mother • National > local authority (LA) but subnational data restricted to 5 year age-groups • Census or mid-year estimates provide populations at risk

21. Geographic variation in ethnic fertility • Child : Woman Ratios (CWRs): an indicator of family size • Census data for each LA for each ethnic group • Children aged 0-4 / Women aged 15-44 • For each location: • TFR(e) = TFR(aw) * ( CWR(e) / CWR(aw) ) • Where: e = Ethnic group & aw = All women

22. Geographic variation in ethnic fertility • Estimates of TFRs using CWRs • But (1) … • These population counts do not link children and mothers • A child reported as being of ‘Mixed’ ethnicity may have a ‘White’ mother & a ‘Black’ father • When calculating CWRs, the ‘Other’ ethnicity children (inc. the Mixed) are linked with Other group mothers • This would deflate the White CWR and inflate the Other CWR

23. Geographic variation in ethnic fertility • Estimates of TFRs using CWRs • To correct for lack of child-mother linkage needs a correction factor: • Use the TFRs from CWRs derived from a national coverage microdata survey which links women with their children (as above) • TFR(e) = TFR(aw) * ( CWR(e) / CWR(aw) ) • Then calculate a scale factor: • SF(e) = TFR(e) / TFR(e) • From survey data From population data

24. Geographic variation in ethnic fertility • Estimates of TFRs using CWRs • The estimated TFRs are then based on: • TFR(e) = TFR(aw) * (SF(e) * CWR(e) / CWR(aw))

25. Geographic variation in ethnic fertility • Estimates of TFRs using CWRs • But (2) … • Since minority groups may have very small numbers in some locations consider substituting: • National CWR(e) for the local CWR(e); or • An average of the national CWR(e) and local CWR (aw) • TFR(e) = TFR(aw) * (SF(e) * CWR(e) / CWR(aw))

26. Geographic variation in ethnic fertility Estimates of TFRs using CWRs

27. Age-specific variation in ethnic fertility For each LA … Leeds (1991) Bradford (1991) Scale local ASFR(aw) by National ASFR (e) Scale ASFR(e) by local TFR (e) Calculate births by ethnic groups Fit births to VS Recalculate ASFRs

28. Age-specific variation in ethnic fertility

29. Age-specific variation in ethnic fertility

30. Age-specific variation in ethnic fertility

31. Fertility indicators by ethnic group … • Vital Statistics Geography: national to local • Age: five year detail • Populations • Geography: national to local • Age: five year detail • Ethnicity: up to 16 groups (2001) • Survey • Geography: national (& region) • Age: (SYA &) five year detail • Ethnicity: (15,) 8 & 4 groups (2001)

32. Fertility indicators by ethnic group … • Data shopping list • National level • Births by age of mother, detail by 5 year age-group or ‘better’ • Populations at risk by matching age detail • Large scale survey microdata with age, sex, ‘subgroup’ (ethnicity, religion, race, country of birth) & indicators of presence of dependant child (aged < 5) & ‘generation’ or ‘relationship’ • Subnational level • Births by age of mother, detail by 5 year age-group or ‘better’ • Populations at risk by matching age detail • Populations by ethnic group by 5 year age-group

33. Fertility indicators by ethnic group … Data shopping list Ethnic group detail N.B. Any outputs are estimates … Could be tenure, religion, social class, qualifications …