Estimating Migration from Census data Issues for consideration By Richmond Tiemoko

Outline Definition Issues emerging Data requirements International Migration Internal Migration

Definition According to the United Nations recommendations, migrants consist of four categories:  - long-term immigrants (or emigrants); - short-term immigrants (or emigrants);  - residents returning after (or leaving for) a period working abroad, i.e. short-term emigrants returning (or leaving); and - nomads. Long term Migrant: A person who moves to a country/place of usual residence other than that of his or her usual residence for a period of at least a year (12 months), so that the country/place of destination effectively becomes his or her new country/place of usual residence. From the perspective of the country of departure the person will be a long-term emigrant and from that of the country of arrival the person will be a long-term immigrant.

Migration data and information Provided that the census(es) gather the appropriate information and are reasonably accurate it is technically straight forward to estimate migration from census data . It is possible to produce estimates of: Stock of Migrants (in-migration, emigrants?) Net immigration (i.e. immigration less emigration) of the foreign-born population (people born outside a particular country) Internal migration between sub-national regions of a country, over the period between two censuses. Stock of out-migrants Migrants as a percentage of total population Females (specific population group) among migrants Migrants by age group Migrants by socioeconomic characteristics.

Migration and Mobility Issues emerging from census generated migration data Mobility Displaced and forced migration Return migration Citizenship and Stateless

Data Requirements Usual Census Questions for migration study: Place of birth Place of residence Nationality/ Citizenship Place of previous Residence Duration of residence ( Flow) Date of Migration

Data Requirements (cont…) To estimate net immigration of foreigners*: the number of foreign-born females (males), in five-year age groups, and for an open age interval A+, at two points in time, typically two censuses For the deaths: either a suitable model life table or the numbers of native-born females (males), in five-year age groups, and for an open age interval A+, at two points in time, typically two censuses. Failing these, the central crude death rate for the population To estimate sub-national regional net in-migration from place of birth data: the number of females (males) by sub-national region and by sub-national region of birth, in five-year age groups, and for an open age interval A+, at two points in time, typically two censuses The concept of Foreigner is a social and legal concept. It can affect the estimate of migration for example for people born to migrant

Data Requirement (cont…) To estimate internal migration between sub-national regions from place of residence at previous census data: The numbers of females (males) by sub-national region and by sub- national region at some prior date, typically that of the preceding census, in five-year age groups, and for an open age interval A+. If age-specific numbers are not available, aggregated data is still useful for estimating all-age migration.

Data quality and preparation Evaluate the data quality (age and sex distribution) . Difference with general population, host country population Change in boundaries at sub-national or international levels Net migration, by definition, underestimates the flows of migrants into and out of a region or country. Thus, for example, return migration and mobility within the period being considered will result into zero net migration.

Estimating Net migration using the place of birth Step 1: Decide on survival factor If data on the number of foreign-born people in the population are available by age group for each census then one needs to estimate the survival factors to be applied to the numbers of foreign-born in the first census to estimate the numbers surviving to the time of the second census. Use a life table Steps 2: Estimate the number of deaths of immigrants

Step 3: Estimate the net number of immigrants (of foreigners) If data are available by age group for each census then age-specific net immigration can be estimated as follows:  Net ​5MFx=​5NFx+n(t+n)−​∞NFx(t)+​5DFx  for x = 0, 5, … , A-5-n where  Net ​5MFx  represents the net number of immigrants between times t and t+n who were aged between x and x + 5 at time t. For x > A - 5 - n;  Net ​∞MFA−n=​∞NFA(t+n)−​∞NFA−n(t)+​∞DFA−n . The net number of immigrants of those born between times t and t+n is estimated as follows:  Net ​MFB=​nNF0(t+n)+​DFB . If data and/or survival factors are not available by age group then estimate The total net number of immigrants as follows:  Net ​∞MF0=​∞NF0(t+n)−​∞NF0(t)+​∞DF0 .

Example: Table 1 Estimation of deaths of foreign-born and the net number of immigrants by age group, South Africa, 2001-2006 Age 2001 2006 x 5Sx Age at 2ndcensus DF Net M   B 0.94151 0- 4 8,963 12,577 0.97896 391 12,968 5- 9 10,390 13,724 5 0.99547 242 5,003 10-14 13,508 13,998 10 0.99427 55 3,664 15-19 27,835 27,943 15 0.98602 119 14,555 20-24 69,787 59,493 20 0.96458 616 32,275 25-29 87,381 95,763 25 0.93161 2,994 28,970 30-34 73,338 100,450 30 0.90960 6,675 19,743 35-39 66,663 85,490 35 0.89780 7,563 19,715 40-44 59,152 75,684 40 0.89092 7,701 16,721 45-49 45,184 66,113 45 0.88633 7,274 14,234 50-54 40,398 55,913 50 0.87224 6,154 16,883 55-59 30,640 42,833 0.84731 5,717 8,153 60-64 24,376 34,433 60 0.80885 5,442 9,234 65-69 17,895 25,588 65 0.75468 5,353 6,564 70-74 13,561 18,989 70 0.66991 5,281 6,375 75-79 10,238 12,850 75 0.56388 5,404 4,693 80-84 7,658 7,461 80+ 0.40912 5,118 2,341 85+ 4,455 5,305 7,410 602 Total 611,423 754,608 79,509 222,693

Estimating Net internal Migration Indirect Methods Net M = (Pt+n)-Pt.- (B-D) Survival Ratios Methods: Net M'(x) = Px+.n,t+.n-S·PX,1 The basic information required is the number of persons classified by age and sex as enumerated in each area at two successive censuses and a set of survival ratios which can be applied to the population at the first census in order to derive an estimate of the number of persons expected to survive to the second census 3.Census Survival Ratios (CSR) if you have strong reason not to use life table.

Estimating net internal migration between sub-national regions from place of birth data Estimation process similar to the one of foreign born migration Change in the number of population born in the region and living outside the region gives the estimate of net out-migration from that region Subtracting this from the net in-migration of those born outside the region gives an estimate of the overall net in-migration into the region

Estimating internal migration between sub-national regions from place of residence at previous survey Net sub-national regional migration is estimated directly from the numbers of people in each region at the time of the census who moved since the previous census by region they were in at a given prior date (e.g. at the time of the previous census). where the superscript (’) represents numbers surviving and 5I’x and 5O’x respectively represent the number of surviving in-migrants into, and the surviving number out-migrants from, a particular region at the time of the second census who were aged between x and x+5 at the second census The number of migrants is derived from the number of surviving in- and out-migrants as follows:   5Mx=(​5I′x−​5O′x+(​5I′x−​5O′x)x/​5Sx)/2 ,

THANK YOU Example and Questions