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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.

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slide1

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
slide2

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
slide3

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)
slide4

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

slide5

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

slide6

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

slide7

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

slide8

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
slide9

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)
slide10

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
slide11

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
slide12

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
slide13

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)
slide14

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
slide15

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 …
slide16

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)
slide17

Age-specific variation in ethnic fertility

  • Use TFRs from CWRs to scale the curves for overall level & to add ethnic detail
slide18

Age-specific variation in ethnic fertility

  • Calculate numbers of births

Scale births

slide19

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 …
slide20

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
slide21

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
slide22

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
slide23

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
slide24

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))
slide25

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))
slide26

Geographic variation in ethnic fertility

Estimates of TFRs using CWRs

slide27

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

slide31

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)
slide32

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
slide33

Fertility indicators by ethnic group …

Data shopping list

Ethnic group detail

N.B. Any outputs are estimates …

Could be tenure, religion, social class, qualifications …