qmss2 immigration & population dynamics: summer school projection methods for ethnicity and...

QMSS2 Immigration & Population Dynamics: Summer School

PROJECTION METHODS FOR ETHNICITY AND IMMIGRATION STATUS

The estimation of ethnic fertility

Paul NormanSchool of GeographyUniversity of Leeds

Acknowledgements

• ESRC, ONS, GROS, NISRA, OS, UKBORDERS, CDU

http://www.esrc.ac.uk/

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 womenFertility 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)

England & Wales <20 20-24 25-29 30-34 35-39 40+ Total

Births during 2001 44178 108806 159861 178817 86454 16244 594360

Mid year population 'at risk' 1578418 1577685 1744662 2033424 2081985 1853349 10869523

<20 20-24 25-29 30-34 35-39 40+ TFR

ASFRs 27.99 68.97 91.63 87.94 41.52 8.76 1.63

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Fertility rates in a projectionProjections 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

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<20 20-24 25-29 30-34 35-39 40+

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

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<20 20-24 25-29 30-34 35-39 40+

a.) TFR = 1.69

b.) TFR = 1.44

N.B. Can have same TFR for different shape of curveTFR ‘just’ a summary measure

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

Age-specific variation

England & Wales

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1981 1986 1991 1996 2001 2006

Year TFR

1981 1.79

1986 1.77

1991 1.83

2001 1.74

2006 1.85

Geography needed

Bradford

Leeds

Subnational variations in fertility

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<20 20-24 25-29 30-34 35-39 40+Age

Ag

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1991

2001

2006

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1981

1991

2001

2006

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

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 riskASFRs & 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


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 populationWomen 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 15-44

TFR(e) = TFR(aw) * ( CWR(e) / CWR(aw) )

Where: e = Ethnic group & aw = All women


White BlackCarribean

BlackAfrican

Indian Pakistani Bangladeshi Chinese Others All women

CWR 0.1369 0.1475 0.1687 0.1147 0.1288 0.1849 0.1183 0.1086 0.1360

Scaled TFRs 1.64 1.77 2.02 1.37 1.54 2.22 1.42 1.30 1.63

Simple crosstabs …• Presence of dependant child by age of mother & ethnic group

• Age-specific rates spiky (even with broader groups)


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White Black South Asian Chinese & Others

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


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White Black South Asian Chinese & Others

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 …


0.0000

0.0050

0.0100

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0.0200

0.0250

0.0300

151617181920212223242526272829303132333435363738394041424344

White

Black

South Asian

Chinese & Others

Total

0.00

0.01

0.01

0.02

0.02

0.03

0.03

15-19 20-24 25-29 30-34 35-39 40-44

White

Black

South Asian

Chinese & Others

Total

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)


Probabilities <20 20-24 25-29 30-34 35-39 40+White 0.04 0.23 0.23 0.22 0.10 0.04Black 0.10 0.25 0.27 0.21 0.09 0.07South Asian 0.01 0.20 0.26 0.23 0.08 0.02Chinese & Others 0.03 0.12 0.20 0.16 0.13 0.03All women 0.04 0.22 0.22 0.22 0.10 0.04

England & Wales <20 20-24 25-29 30-34 35-39 40+ TFRASFRs 27.99 68.97 91.63 87.94 41.52 8.76 1.63

Step 1 15-19 20-24 25-29 30-34 35-39 40-44 TFRWhite 28.97 71.36 94.56 88.71 41.53 8.78 1.67Black 64.89 77.88 112.51 85.68 38.61 16.04 1.98South Asian 7.10 62.30 106.26 94.49 32.83 5.24 1.54Chinese & Others 17.93 36.31 81.48 63.96 54.16 6.47 1.30All women 27.99 68.97 91.63 87.94 41.52 8.76 1.63

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


Step 1 15-19 20-24 25-29 30-34 35-39 40-44 TFRWhite 28.97 71.36 94.56 88.71 41.53 8.78 1.67Black 64.89 77.88 112.51 85.68 38.61 16.04 1.98South Asian 7.10 62.30 106.26 94.49 32.83 5.24 1.54Chinese & Others 17.93 36.31 81.48 63.96 54.16 6.47 1.30All women 27.99 68.97 91.63 87.94 41.52 8.76 1.63

Step 2 15-19 20-24 25-29 30-34 35-39 40-44 TFR TFRs(CWR)White 28.47 70.13 92.93 87.18 40.81 8.63 1.64 1.64Black Carribean 57.99 69.60 100.55 76.58 34.51 14.33 1.77 1.77Black African 66.34 79.62 115.02 87.60 39.48 16.40 2.02 2.02Indian 6.33 55.57 94.78 84.29 29.28 4.68 1.37 1.37Pakistani 7.11 62.43 106.47 94.69 32.89 5.26 1.54 1.54Bangladeshi 10.21 89.58 152.79 135.87 47.20 7.54 2.22 2.22Chinese 19.53 39.55 88.75 69.67 59.00 7.04 1.42 1.42Others 17.94 36.33 81.52 64.00 54.20 6.47 1.30 1.30All women 27.92 68.79 91.40 87.72 41.42 8.74 1.63 1.63

• Calculate numbers of births


Step 3Population at Risk <20 20-24 25-29 30-34 35-39 40+ TotalWhite 1372984 1368197 1531796 1810020 1878809 1686574 9648379Black-Caribbean 19234 16571 19324 32476 41714 30583 159902Black-African 20092 20867 26283 33285 29181 19646 149355Indian 43969 47406 49701 48525 43647 42427 275674Pakistani 37694 39651 34987 31044 20214 20111 183700Bangladeshi 15767 17229 16164 10557 6614 5232 71564Chinese 12053 15329 11861 10750 10838 10517 71347Other 56625 52434 54547 56767 50970 38257 309601Total 1578418 1577685 1744662 2033424 2081985 1853349 10869523

Estimated births <20 20-24 25-29 30-34 35-39 40+ TotalWhite 39093 95954 142349 157790 76675 14553 526413Black-Caribbean 1115 1153 1943 2487 1440 438 8577Black-African 1333 1661 3023 2916 1152 322 10407Indian 278 2635 4711 4090 1278 198 13190Pakistani 268 2475 3725 2939 665 106 10179Bangladeshi 161 1543 2470 1434 312 39 5960Chinese 235 606 1053 749 639 74 3357Other 1016 1905 4447 3633 2762 248 14011Total 43500 107933 163720 176038 84923 15979 592093

VS Births 44178 108806 159861 178817 86454 16244 594360

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 …


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White Black Carribean Black African Indian

Pakistani Bangladeshi Chinese Others

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

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Bradford Leeds

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:


Where: e = Ethnic group & aw = All women

Geographic variation in ethnic fertility

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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 fertilityEstimates 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)


Then calculate a scale factor:

SF(e) = TFR(e) / TFR(e)

From survey data From population data

Geographic variation in ethnic fertilityEstimates of TFRs using CWRs

The estimated TFRs are then based on:

TFR(e) = TFR(aw) * (SF(e) * CWR(e) / CWR(aw))

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Adjusted Unadjusted


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))




Leeds White Black-Caribbean Black-African Indian Pakistani Bangladeshi Chinese Other All women TFR

CWR 0.248 0.305 0.190 0.251 0.330 0.358 0.259 0.285 0.253 1.44

Estimated TFR 1.41 1.73 1.08 1.42 1.87 2.03 1.47 1.62

Bradford White Black-Caribbean Black-African Indian Pakistani Bangladeshi Chinese Other All women TFR

CWR 0.282 0.290 0.331 0.342 0.366 0.429 0.303 0.358 0.331 2.17

Estimated TFR 1.84 1.90 2.16 2.23 2.39 2.81 1.98 2.34

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White Black-Caribbean Black-African Indian

Pakistani Bangladeshi Chinese Other


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

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White

Black-Caribbean

Black-African

Indian

Pakistani

Bangladeshi

Chinese

Other

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Bangladeshi

Chinese

Other

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White

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Black-African

Indian

Pakistani

Bangladeshi

Chinese

Other

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91

White

Black-Caribbean

Black-African

Indian

Pakistani

Bangladeshi

Chinese

Other

0

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91

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91

Leeds (1991) Bradford (1991)


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BirthsWhite 4552Indian 270Pakistani 1917





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


Data shopping list

Ethnic group detail

N.B. Any outputs are estimates …Could be tenure, religion, social class, qualifications …


qmss2 immigration & population dynamics: summer school projection methods for ethnicity and...

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