In-depth Analysis of Census Data on Migration Country Course on Analysis and Dissemination of Population and Housing Census Data with Gender Concern October 2011, Jakarta, Indonesia

Outline Migration as a Demographic Component Definition of Migration Types of Migration –Internal and International Sources of migration data Direct Measures of Migration Indirect Measures of migration Measurements of migration Place of Birth (POB) method Vital statistics method using demographic Balancing equation Survival ratio methods Forward survival method Reverse survival method

Migration as a Demographic Component ( Demographic Component/ Demographic Dynamics/ Demographic process): Migration is a demographic component that determine the size, growth, distribution and composition of population. Migration – Migration is a movement from one geographical area to another geographical area crossing the administrative boundaries for permanent or semi permanent residence. The starting place is known “place of origin” whilst the ending place is called ‘place of destination’. - Internal Migration (migration within a country) - External or International migration ( migration between countries)

Form of Internal and international Migration Form of Internal Migration:  Rural to Urban (Rural – urban migration)  Urban to Rural (Urban – rural migration)  Rural to Rural (Inter- rural migration)  Urban to Urban (Inter – urban migration) Form of International Migration  Developing country to Developed  Developing to Developing country  Developed to Developing country  Developed to developed country

Classification of Migration & Migrants Life – time migration (The place of birth is different from place of residence). Recent – migration (The place of current residence is different from the place of previous residence) POB Method id the way of deriving the life – time migration or ever migration. A cross – tabulation of Previous versus current residence is the way of deriving the recent migration. Mass migration, force migration, return migration, labour migration are the other groups of categories of migration.

Sources of migration data Population censuses Population registers Sample surveys International migration statistics records Other sources

Measures of Migration Direct Measures: In-migration Rate (IR): the number of in-migrants to a physical/administrative area in a given year. IR= The number of in-migrants to an area in given year x 1000 Mid year population Out-migration Rate (OR): the number of out-migrants departing an area of origin, per 1,000 population at that area of origin in a given year. OR = the number of out-migrants in a given year x 1,000 Mid year population

Net Migration Rate (NMR): the net effect of in- migration and out-migration on an area’s population, expressed as increase or decrease per 1,000 population of the area in a given year. NMR= Number of inmigrants-outmigrants x1000 Mid year population or NRR = IR – OR Gross Migration Rate: the total number of in-migrants and out-migrants per 1,000 population of the area in a given year GMR = IR + OR The above measures can be calculated for Gender as well.

Indirect measures of migration Why we need indirect measures: Unavailability of data for a small unit Defective of data Calculation to be made for specific concern To appraise the quality of migration data in a Census. To project the migration by age or for future

Cont... Benefits of indirect migration estimates They can provide information through time, including data for period and places where no other migration statistics available They are applicable at all geographical levels from local to regional and national populations Some of the methods provides estimates by age and sex Comparing estimates derived from different methods, can be used to validate findings and the quality of data

Vital statistics method simplest and potentially most accurate method of estimating net migration The Demographic Balancing equation can be used Net migration is obtained for each district/ region/area by subtracting natural increase from the total population change

Vital statistics method simplest and potentially most accurate method of estimating net migration The Demographic Balancing equation can be used Net migration is obtained for each district/ region/area by subtracting natural increase from the total population change

Cont… Demographic Balance Equation Net Migration = ( P(t+1)- P(t))+Natural Increase or, (Immigrants-Emigrants) = (P(t+1)- P(t) )+(Births- Deaths)

Cont… Accurate estimation of net migration by this method require accurate vital statistics on births and deaths together with reliable census statistics or other data on population change Develop countries vs. developing countries

Survival ratio methods Survival ratio methods i nvolve 2 main steps 1. Calculate how many in a birth cohort survive from one census to the next 2. Subtract the number of survivors from the cohort’s size at the second census The difference is the intercensal net migration

Cont… These estimates are usually do separately for males and females to account age sex related variations in probabilities of moving Data for survival ratio methods A sets of age – sex specific survival ratios Statistics on population by age and sex at two consecutive censuses (5 year or 10 year)

Cont… Calculation of age –sex specific net migration A B C D=(C-B) Total Aged males in 2000 Survivors aged in 2005 Total Aged 30-34, males in 2005 Net migration Ages 30-34, males

Survival ratio methods Forward survival method work forward through time Reverse survival method Work backward through time

Forward survival method Estimate the net migration at the end of the interval (i) Net migration gain Net migration gain Cohort population size ages size age Estimated survivors 5 years

Cont… Forward survival method (ii) Net migration loss Net migration loss Cohort population Estimated survivors size ages Cohort population size age years

Cont… To estimate the net migration of people aged at the end of the period, the estimated survivors (from the original cohort, by using survivorship probabilities) are subtracted from the total census population (second census) aged in the area The estimated survivors from the initial cohort age 20-24, exceeded the census counts of year old in the second census, that means due to migration, increase the cohort size or net migration gain to that area

Cont… The formula for forward survival estimates of net migration is (Shryock and Siegel,1973): Net M ′ x+n = P ⁿ x+n – S x P0 x Where Net M ′ x+n is the estimated net migration for the end-of-period population age x+n n is the interval in years between 2 censuses P0x is the initial population aged x P ⁿ x+n is the end-of-period population aged x+n S is the survival ratio from age x to x+n

Reverse survival method Provide a more complete estimate of the volume of net migration, especially when the migration interval is long or mortality is high Reverse survival usually produces higher estimates of net migration because the figures include migrants who died Start with the end period ages from reverse survival estimates, because some of the migrants would have died Reverse survival refers to migrants’ initial age

reverse survival method (i) Net migration gain Net migration gain Cohort population size ages size age Expected initial population 5 years

reverse survival method (i) Net migration loss Net migration loss Cohort population size ages size age Expected initial population 5 years

Cont… The formula for reverse survival estimates of net migration is 1 Net M ′ x = ---- x P ⁿ x+n – P0x S Where Net M ′ x is the estimated net migration for the initial population age x, obtained by reverse survival n is the interval in years between 2 censuses P0x is the initial population aged x P ⁿ x+n is the end-of-period population aged x+n is the reciprocal of the survival ratio from age x to x+n S

Reverse survival is obtained by multiplying end –period population by the reciprocal of the survival ratio (i.e. 1/survival ratio) and subtracting the initial population E.g. if 5-9 age cohort size = 500 and S x = The number of survivors = 500 x = Using reverse The expected initial cohort size will be x (1/ ) =500 migration estimates.xls

The birth place method Cross-tabulation of migration status & characteristics Place of Usual Residence (POR) by Place of Birth (Birth place method) -life time migration moves only - severe underestimation migration moves as intermediate destinations are not recorded POR by POR 1 or 5 years ago - focus on recent migration flows

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