United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Evaluation of Internal Migration Data Collected from Population Censuses
United Nations Statistics Division
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Outline
- Related concepts of internal migration
- Direct and indirect estimates of internal migration
- Sample tabulations
- Discussion on quality issues
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration – related concepts
- Mobility versus migration
- Migration refers to “long-distance” move, i.e., moves across states or county lines (usually referring to across administrative unit borders)
- Migration change of place of usual residence
- Time element
- Geographic moves
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration – related conceptshort and long distance moves
Data source: Methods and Materials of Demography, classification based on “1-year” data from the March 2000 Current Population Survey of the US
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Place of usual residence (UN, 2008)It is recommended that countries apply a threshold of 12 months when considering place
of usual residence according to one of the following two criteria:
(a) The place at which the person has lived continuously for most of the last 12 months (that is, for at least six months and one day), not including temporary absences for holidays or work assignments, or intends to live for at least six months;
(b) The place at which the person has lived continuously for at least the last 12 months, not including temporary absences for holidays or work assignments, or intends to live for at least 12 months.
Difficult to treat groups:- Seasonal residence- work in one place during weekdays and join family member during weekends- College students
Internal migration – related concepts (2)
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration – related concepts (3)
Lifetime migration:
- Migration occurred between birth and the time of the census
Recent migration:
- Migration occurred in recent period, e.g., 1 year
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses
- Tabulated from direct questions about mobility or about prior residence- Place of birth- Place of residence at a fixed past date- Duration of residence- Previous place of residence
- Estimates of net migration derived from (residual estimates)- Counts of total population or population disaggregated by age and
sex, at two censuses- Natural increase or intercensal survival rates, which are derived in
turn from (a) life tables or (b) comparison of the age distributions of countries not experiencing immigration or emigration in successive censuses
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct method
- Place of birth- Civil division of birth for native-borns; usually refers to the geographical unit of the
country in which the mother resides at the time of the person’s birth- Country if foreign-born
- Place of residence at a specified date in the past- Major or smaller division, or a foreign country- 1 or 5 years, or both- 1 year easier to recall- Different date may be used depends on national circumstances
- Duration of residence- Should refer to the length of residence in the major or smaller civil divisions and the
locality, but not in the particular housing unit
- Place of previous residence- Major or smaller division, or a foreign country
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodplace of birth (1)
Source: The Methods and Materials of Demography, 2nd edition, Siegel and Swanson, 2004
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodplace of birth (2)
Source: The Methods and Materials of Demography, 2nd edition, Siegel and Swanson, 2004
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Intercensal migration can be estimated by using data by place of birth from two consecutive censuses
Net migration for an area M = (It+n-Ot+n) – (S1It – S2Ot )
It: life time in-migrants at time t
It+n: life time in-migrants at time t+n
Ot: life time out-migrants at time t
Ot+n: life time out-migrants at time t+n
S1: proportion of life time in-migrants It that will survive to time t+n
S2: proportion of life time out-migrants t that will survive to time t+n
Internal migration data from censuses – direct methodplace of birth (3)
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodplace of birth (4)
Source: Manual VI: Methods of Measuring Internal Migration, United Nations, 1970
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodplace of birth (5)
Quality issues:
- Memory problem
- Uncertainties about area boundaries at the time of birth
- Errors in reporting of birthplaces for babies who were not born at the usual residence of their parents
- Reporting birthplace according to the old administrative boundaries
- Reporting place of births like hospitals rather than place of usual residence of the mother
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct method place of birth (6)
Ways to assess data quality:
- re-interviews or matching studies of a sample of the original records (US census Bureau, 1995, p.19)
- Study the impact of boundary changes:
- Lee et al. 1957
- Compare between censuses or with household surveys
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodresidence at a fixed past date (1)
Source: Statistics Bureau of Japan
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodresidence at a fixed past date (3)
Information may be used to get a sense of “flow”: annual in-migrants and out-migrants for different areas.
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodresidence at a fixed past date (4)
Quality issues:
- Memory problem, the longer the period used, the less accurate the information is
- Mis-reporting of previous residence
- Change of boundaries
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodduration of residence + previous residence (1)
Distribution of lifetime migrants by duration of stay in each State
Source: Manual VI: Methods of Measuring Internal Migration, United Nations, 1970
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct method duration of residence + previous residence (2)
For recent migrants: longer distance more migrants
Source: Manual VI: Methods of Measuring Internal Migration, United Nations, 1970
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodduration of residence + previous residence (3)
Origin, destination and time of migration (duration):
Source: Manual VI: Methods of Measuring Internal Migration, United Nations, 1970
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – direct methodduration of residence + previous residence (4)
Quality issues:
- Memory problem, might not remember when moved
- Digit preference (similar to those reflected in age-reporting)
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – indirect method National growth rate method (1)
• National growth rate method – for net internal migration
001001 /)(/)( tttiiii PPPPPPm Population of area i in the first census
Population of area i in the second census
Total population of a country in the first census
Total population of a country in the first census
0iP
1
0
1
t
t
i
P
P
P
Positive rate: with net inmigration; negative rate: net outmigration Assumes same natural increase rate and net immigration from abroad for
all parts of the country
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
• National growth rate method – example
Population
Rate of Net Internal Migration2001 1991
Austria: Burgenland 277569 270880 -0.0057
Austria: Corinthia 559404 547798 -0.0092
Austria: Lower Austria 1545804 1473813 0.0184
Austria: Salzburg 515327 482365 0.0379
Austria: Styria 1183303 1184720 -0.0316
Austria: Tirol 673504 631410 0.0363
Austria: Upper Austria 1376797 1333480 0.0021
Austria: Vienne 1550123 1539848 -0.0237
Austria: Vorarlberg 351095 331472 0.0288
Austria: Total 8032926 7795786
Internal migration data from censuses – indirect method National growth rate method (2)
Data source: graph produced based on data from United Nations Demographic Yearbook
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Vital statistics method for net migration rate 0001 /)(/)( tttiiii PDBPPPm
Births nationally during the intercensal period
Deaths nationally during the intercensal periodt
t
D
B
Assumes same natural increase rate across all areas
Calculate net migration rate (incl. both internal and international migration)
Internal migration data from censuses – indirect method Vital statistics method (1)
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Population
Rate of net migration2001 1991
Austria: Burgenland 277569 270880 0.0159
Austria: Corinthia 559404 547798 0.0124
Austria: Lower Austria 1545804 1473813 0.0401
Austria: Salzburg 515327 482365 0.0596
Austria: Styria 1183303 1184720 -0.0100
Austria: Tirol 673504 631410 0.0579
Austria: Upper Austria 1376797 1333480 0.0237
Austria: Vienne 1550123 1539848 -0.0021
Austria: Vorarlberg 351095 331472 0.0504
Austria: Total 8032926 7795786
Vital statistics method – example
Internal migration data from censuses – indirect method Vital statistics method (2)
Data source: graph produced based on data from United Nations Demographic Yearbook
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Survival-rate method
ssPPM xt
txtx
x )( 0
Net migration for the cohort aged x at year 0 to year t
Population size for cohort x (at year 0) at year t
Survival rate of the cohort from year 0 to year t
Population size for cohort x at year 0
Adjustment for deaths of migrants during the periods
P
s
P
M
x
ttx
txx
0
s can be calculated by x
xL
L5
105
Internal migration data from censuses – indirect method Survival rate method (1)
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Internal migration data from censuses – indirect methodSurvival rate method (2): Vienna, Austria
AgePopulation in
199110-year life table
survival ratio Age Population in 2001 expected survivors Net migration
(1) (2) (3) (4) (5) (6) = (2)*(3) (7) = (5) - (6)
0 - 4 39,766 0.99622529 10 - 14 38,867 39616 -749
5 - 9 36,574 0.991467948 15 - 19 38,979 36262 2,717
10 - 14 34,289 0.988364131 20 - 24 42,705 33890 8,815
15 - 19 40,166 0.987782981 25 - 29 54,108 39675 14,433
20 - 24 62,313 0.985758641 30 - 34 69,222 61426 7,796
25 - 29 72,289 0.980066411 35 - 39 71,228 70848 380
30 - 34 62,655 0.969033736 40 - 44 59,845 60715 -870
35 - 39 51,290 0.951866079 45 - 49 49,023 48821 202
40 - 44 56,236 0.927062515 50 - 54 51,774 52134 -360
45 - 49 56,240 0.886929277 55 - 59 49,495 49881 -386
50 - 54 48,941 0.826409977 60 - 64 41,373 40445 928
55 - 59 32,213 0.749135574 65 - 69 25,381 24132 1,249
60 - 64 33,819 0.639850773 70 - 74 24,730 21639 3,091
65 - 69 30,831 0.488011131 75 - 79 19,593 15046 4,547
70 - 74 19,021 0.399270089 80 - 84 9,472 7595 1,877
75 - 79 18,050 0.33555271 85 - 89 5,486 6057 -571
80 + 19,832 0.204715764 90+ 2,336 4060 -1,724
All ages 714,525 Total 10+ 653,617 612241 41376
Tabulated based on data obtained from Austria Statistics Office online database
United Nations Sub-Regional Workshop on Census Data EvaluationPhnom Penh, Cambodia, 14-17 November 2011
Possible concerns/errors to use indirect method
• Change of area boundaries
• Mixture with international migration
• Depends on errors in all components:
• Population by age and sex
• Births
• Deaths
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