UNFPA/UNECE/NIDI Training programme on international migration, Geneva, 24-28/01/2005

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UNFPA/UNECE/NIDI Training programme on
international migration, Geneva, 24-28/01/2005
Analytical Measures and Methods George
Groenewold, NiDi 1. Demographic Balance
Equation 2. Method related concepts and
definitions 3. Main approaches A. Migration
status is known direct methods A.1 Cross-tabula
tion migration status characteristics and an
example B. Migration status is unknown
indirect methods B.1 Vital Statistics or
Residual Method and an example B.2 Intercensal
Cohort Component Method and an example
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1. The Demographic Balance Equation P(t1)
P(t)Births-Deaths(Immigrants-Emigrants), or,
P(t1) P(t)Natural IncreaseNet Migration
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2. Method related concepts and definitions
Out-migration (emigration) rate number of
persons that moved out of place X divided by the
average number of persons that were exposed to
migration In-migration (immigration) rate
number of persons that live in place x, but
originated from elsewhere, divided by the average
number of persons that were exposed to
migration Net migration the difference between
the number of immigrants (or in-migrants) and the
number of emigrants (or out-migrants) Note no
concensus about which persons should be in the
denominator in the above measures (UN, 1970,
pp40-42.), depends on research question which
one to choose Lifetime migrant someone who at
the time of the census lives away from his/her
place of birth
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Cohort A cohort is a group of individuals
experiencing the same demographic (vital) event.
Birth cohortpersons born in the same year.
Migration cohortpersons who emigrated from
country X in the same year. Life table. A
life-table summarizes the (age specific)
mortality experience in a population in a
particular year or particular (intercensal)
period. Separate life tables are constructed for
men and women. A full life-table can be derived
from a set of Age Specific Mortality Rates
(ASMRs). Two important products of the life
table are (1) the life expectancy at birth and
(2) age-specific survival ratios Survival
Ratio. Indicator for the probability of surviving
of persons in a particular age-group X to the
next higher age-group X5. Survival ratios are
used in cohort component projections of the
population Cohort Component Projection Method.
Estimation method that builds on the principle
that the size and age-structure of the current
population can be predicted from an age
distribution in the past if interperiod births,
deaths and net numbers of (international)
migrants are known
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• 3. Main approaches
• A. Migration status is known direct method (D)
• A.1 Cross-tabulation of migration status
  characteristics
• Place of Usual Residence (POR) by Place of Birth
• -life time migration moves only, not
  time-specific
• -severe underestimation migration moves
  (intermediate destinations not recorded)
• POR by POR 1 or 5 years ago Example
• -focus on recent migration flows
• -UN recommends 5 years ago
• -recall problem with fixed reference date
• POR by Place of Previous Residence by Duration
  of Residence
• -refined migration cohort analysis, and
  migration and development analysis
• - recall problem

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Table 1. Place of (usual) residence at time of
census by Place of residence 1 year ago
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Table 1. (continued)
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Table 1. (continued)
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Table 1. (continued)
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B. Migration status is unknown indirect
methods B.1 Vital Statistics or Residual Method
and an example Demographic Balance
Equation P(t1) P(t)Births-Deaths(Immigrants-Em
igrants), or, P(t1) P(t)Natural IncreaseNet
Migration or, Net MigrationP(t1) -
(P(t)Natural Increase) Indirect estimation
Migration estimate derived as residual from
two subsequent census populations and intercensal
natural increase (recorded or estimated
intercensal births-deaths)
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Table 2. Derivation of net migration estimates if
population figures at two points in time are
known and numbers of births and deaths are known
between these points in time
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Table 2. (continued)
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Table 2. (continued)
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• B.2 Intercensal Cohort Component Method and an
  example
• Data needs
• - Age distributions by sex of two consecutive
  censuses
• - intercensal life-tables by sex
• - Estimate of intercensal fertility (ASFR by
  sex, or ASFR and sex ratio at birth
• The principle
• 1. Project age groups (0-75 years) in first
  census, in year t, to the date of the second
  census using appropriate intercensal life tables
  for each 5- year projection interval
• P(t,x) S(x, x5)P(t5,x5), where xage-group
  
• 2. Estimate births in 5-year projction interval
  and project number of surviving births in each
  5-year projection interval
• 3. Repeat (1. ) and (2.) for each five-year
  projection interval and substract the projected
  population at the time of the second census from
  the observed census population to obtain age
  specific and total net migration estimate
  (indirect or residual estimation)

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Figure 1. Lexis-diagram, illustrating the
principle of Cohort Component Projections
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Step 1 derivation/selection of an appropriate
life table
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Step 2 Estimation of Births and births surviving
projection interval




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Step 3 Derivation of age-specific net-migration
estimates, assuming that second census is
five-years later than first census
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• If census is 10 years apart, add another
  projection interval, I.e. repeat steps 2 and 3
  to determine projected population 10 years later.
  Use different fertility and/or mortality rates
  if appropriate
• This approach may slightly over- or
  underestimate the above age- specific net
  migration numbers
• Solution
• 1. Reverse survive the survivors observed in the
  second census to the date of the first census
  and derive estimate of net number of migrants
  from that projection.
• 2. Average the forward and reverse-survived
  estimate of age-specific net migration
• For Cohort Component Projections, use software,
  e.g.
• - PEOPLE -FiVFiV
• - PAS -LIPRO
• - DemProj - PDPM_PC - MortPak-Lite

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Suggested literature.