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

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 Projections by ethnic groups … why?

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)

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 a.) TFR = 1.69 b.) TFR = 1.44

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

Age-specific information necessary Trends in shape of curve useful in a projection Age-specific variation YearTFR

Geography needed Bradford Leeds Subnational variations in fertility YearTFR YearTFR

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 Fertility rates: data sources …

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

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 Fertility indicators by ethnic group …

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 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 TFR(e) = TFR(aw) * ( CWR(e) / CWR(aw) ) Where: e = Ethnic group & aw = All women 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) 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 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 … 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) Age-specific variation in ethnic fertility

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

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

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 … Age-specific variation in ethnic 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 Geographic variation 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 For each location: TFR(e) = TFR(aw) * ( CWR(e) / CWR(aw) ) Where: e = Ethnic group & aw = All women 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 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 dataFrom population data

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))

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)) Geographic variation in ethnic fertility

Estimates of TFRs using CWRs Geographic variation in ethnic fertility

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

Age-specific variation in ethnic fertility

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

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 Fertility indicators by ethnic group …

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