Center for 
Studies in Demography 
and Ecology

Estimation of International Migration for Vietnam, 1979-1989

by

M. Giovanna Merli
University of Washington

UNIVERSITY OF WASHINGTON			                        CSDE Working Paper No. 97-04

ESTIMATION OF INTERNATIONAL MIGRATION FOR VIETNAM, 1979-1989

M. Giovanna Merli
Center for Studies in Demography and Ecology
Department of Sociology
University of Washington
Tel. (206) 543-2072
email: giovanna@u.washington.edu

March, 11 1997

ESTIMATION OF INTERNATIONAL MIGRATION FOR VIETNAM, 1979-1989

This paper details the various steps adopted in the estimation of international emigration from Vietnam by sex and age between the dates of the first two modern censuses conducted in 1979 and 1989.  The measurement of Vietnamese emigration is based on existing intercensal projection methods.  The procedure is applied to Vietnamese census data to obtain preliminary estimates of Vietnamese intercensal emigration.   A separate estimate of intercensal emigration is derived from a combination of data on the Vietnam-born population in the censuses of the United States, Canada, and Australia, three major receiver countries of Vietnamese emigration, and of data on refugee movements collected by the United Nations High Commissioner for Refugees.  The paper evaluates the two sets of estimates and discusses the relative appropriateness of the data sources for the estimation of intercensal emigration.

Since the end of the Vietnam war and the reunification of North and South Vietnam in April 1975, Vietnam experienced massive streams of outmigration.  The political and economic situation of Vietnam after 1975 drove those closely associated with the US or the South Vietnamese government, Catholics, ethnic Chinese from both north and south Vietnam, and other groups to flee the country.  According to statistics collected by the United Nations High Commissioner for Refugees (UNHCR), since the fall of the Saigon regime in April 1975, about 1.4 million people have left Vietnam.   Of these, 60 percent have left illegally by  boat to whichever Southeast Asian country they would reach first, or overland through Cambodia to Thailand.  The remaining 40 percent have departed directly from Vietnam to resettlement countries after applying to an UNHCR-sponsored program, known as the Orderly Departure Program (ODP), and subscribed by several Western countries.  94 percent of those who left Vietnam have eventually resettled in Western countries (UNHCR, 1995b). 
Recently, official data on the Vietnamese population have become available through the 1979 and 1989 censuses (Vietnam General Statistical Office, 1983; Vietnam Central Census Steering Committee, 1994).  In the absence of a continuous registration system of vital events, the usefulness of two successive census age distributions for demographic analysis is well  known, because the difference between counts of the same cohort at two different points in time, in a closed population, is the result of mortality (United Nations, 1983).  Yet, it is often impossible to arrive to full consistency between census enumerations at two points in time only by accounting for intercensal deaths.  One major obstacle to this effort is successive census enumerations that may be differentially complete.  The second is the lack of information on intercensal net migration on a sex and age specific basis.  Data on international migration in Vietnam are a particularly weak link in this process.  UNHCR counts of refugee movements are so far the only data that allow to gauge levels of Vietnamese emigration.  But, because they only reflect the volume of emigration from Vietnam, and do not provide any information on the age-sex structure of emigrants, they are of limited demographic value.
	This paper attempts to fill this gap, by producing estimates of Vietnam’s international migration by age and sex between October 1, 1979 and April 1, 1989, the two census dates.  These estimates are derived using the residual method for estimating net migration from two census age distributions, a procedure that involves allocating population changes not accounted for by fertility and mortality to migration.  It is first applied to data from Vietnam’s 1979 and 1989 censuses to obtain preliminary estimates of intercensal  net migration.   The method requires that all errors and discrepancies be accounted for prior to defining the residual as net migration.  Differential census enumeration completeness, incomplete registration of births and deaths, or ambiguities as to whether successive census counts include the military population would enter directly in the estimation of net migration if no prior adjustment is made.  In this case, net migration may be confounded with the net balance of errors.  The two Vietnamese censuses were taken at the beginning and at the end of the 1980s, a period characterized by population  redistribution policies and a highly mobile population.  Under these circumstances, it may have been difficult to accurately enumerate persons away from their usual place of residence.  To reduce the risk of bias from these sources, the paper proposes another approach to the measurement of Vietnamese intercensal emigration, one that uses a combination of independent data sources.  Vietnamese emigration can be estimated by referring to information on Vietnamese immigration to the United States (US), Canada, and Australia, three major receiver countries of Vietnamese refugees.  Estimates of Vietnamese immigration to countries of destination are obtained by applying the residual method to Vietnam-born persons enumerated in pairs of successive censuses of the countries of resettlement.  These results are combined with UNHCR counts on Vietnamese refugee movements to yield estimates of intercensal emigration during the period between Vietnam’s two censuses.  The principal objective is the choice of a best estimate that  can be used to adjust one or the other census age distribution for the effects of net international migration during Vietnam’s intercensal period.

PREVIOUS ESTIMATES OF VIETNAMESE EMIGRATION

Emigration from Vietnam to Countries of Resettlement of Vietnamese Refugees 
In the late 1970s, UNHCR established a continuous recording system of monthly and annual counts of arrivals of Vietnamese refugees to camps in “first asylum” countries, resettlement departures to countries of final destination, and counts of departures directly from Vietnam through the ODP.  
	Figure 1 displays annual movements of refugees, by type of movement, and departure, for the period between 1975 and 1995.

[Figure 1 about here]

It is apparent from this figure that the outflow of refugees was marked by dramatic fluctuations. In mid-1976, the number of Vietnamese leaving by boat consisted of a few hundreds per month, but it increased soon thereafter, from about 23,000 in 1976-77 to 30,200 in 1978.  By the end of 1978, there were about 67,000 boat people registered in Southeast Asian refugee camps.  Thereafter, the number of arrivals climbed to a peak, with more than 200,000 in 1979.  This translated to about 150,000 Vietnamese refugee in camps at the end of 1979, as monthly arrivals were not countered by a comparable number of resettlement departures.  The pressure of growing numbers of arrivals to first asylum countries was so strong that some Southeast Asian countries had started to turn away a large number of boats. 
	After a Conference on Refugees was organized in Geneva in July 1979, Western nations’ resettlement pledges resulted in large  numbers of departures from the camps in the second half of 1979 and 1980.  During this period, almost 300,000 boat people departed first asylum countries for their final destinations, with  55,000 persons still awaiting resettlement at the end of 1980, a massive reduction from the large numbers in camps prior to the Geneva conference.
	Arrivals to first asylum countries leveled off to more moderate levels upon the establishment of the ODP program, in June 1979, but they rose again from 21,500 in 1986 to 74,000 in 1989, possibly the effect of a temporary suspension of the ODP in 1986-87.  In 1989, the establishment of a screening process, set up to distinguish true refugees from economic migrants, slowed down the number of arrivals, but also the number of resettlement departures.  After 1988, the total camp population increased again, as the majority of new arrivals were regarded by third countries as economic migrants and denied the right to resettle there.  
	Figure 1 also shows that, while refugees leaving under the auspices of the ODP represented a very small proportion of all Vietnamese refugees until about 1982, for the first time in 1984, they outnumbered boat and land people.  However, only upon definition of the new refugee acceptance criteria  in 1989 did the program come to represent the major channel of departure from Vietnam.  
Of  Vietnamese refugees who resettled to Western countries between 1975 and 1995, 64 percent were accepted by the US, 12 percent went to Australia and 12 percent to Canada.  Among European countries, France received the largest number, although this  number only represents 3 percent of total resettlements (See Table 1).

[Table 1 about here]

	Although UNHCR statistics allow to quantify the volume of Vietnamese emigration, they  are of limited demographic value, as they do not record the demographic characteristics of the refugee population.  Owing to the absence of information on the age-sex structure of the migrant population, these counts cannot be used to adjust one or the other census age distribution for the effects of net migration, and as such are inadequate for analytical purposes.

Emigration from Vietnam to Cambodia
One substantial portion of Vietnamese emigration during Vietnam’s intercensal period consisted of a large number of Vietnamese settlers who crossed the land border to Cambodia following Vietnam’s invasion on Christmas day 1978.  Yet, while UNHCR statistics allow to make some headway towards quantification of the exodus of refugees from Vietnam, the absence of data on Vietnamese emigration to Cambodia during the decade of Vietnamese occupation from Christmas day 1978 to September 1989 is problematic.  Uncertainty surrounds both the magnitude and the timing of the flows. 
 	Ea (1990:10) gives the total number of Vietnamese in Cambodia in 1980 between 300,000 and 500,000.  Kiernan (cited in Banister and Johnson, 1993:97) estimates a national total Vietnamese  population of approximately 350,000.  Banister and Johnson choose a figure of 500,000 Vietnamese settlers because it is in the range of 300,000-700,000 of most estimates of less interested observers.  The figure of 500,000 was also admitted by Phnom Penh officials to the Economist Intelligence Unit (Banister and Johnson, 1993:97).  Nguyen-vo (1992:146) reports that upon withdrawal of Vietnamese troops  in September 1989, there were about  400,000-450,000 Vietnamese settlers in Cambodia.
	One component of Vietnamese migration to Cambodia was return migration of Vietnamese citizens of Cambodia who fled the country between 1970 and 1978, expelled by the Lon Nol government (Ea, 1987: p. 7), the other was new migration of  Vietnamese settlers who established themselves as shop owners, vendors, farmers, or fishermen.  This second component is estimated at about 400,000 (Heuveline, 1996:31).  While the 200,000 Vietnamese troops were gradually withdrawn between 1986 and the end of 1989, it is thought that the an imprecise number of Vietnamese settlers have remained behind (Banister and Johnson, 1993). 
	Even if we believed Banister and Johnson’s preferred estimate of 500,000 Vietnamese arrivals in Cambodia between the end of 1978 and 1989, of which 200,000-300,000 emigrated before the end of 1979 (Ea, 1981:222) and may have not been counted in the 1979 census, we would still be left with 200,000-300,000 people emigrating to Cambodia in the intercensal decade --- and who may have been enumerated in the 1979 census, but not in the 1989 census --- about whom we know nothing.  Some may have eventually reached Thai refugee camps, and may therefore be included in UNHCR counts of Vietnamese land refugee arrivals to UNHCR camps.  According to reports by Vietnamese refugees, crossing the border from Vietnam to Cambodia was not a difficult undertaking, and once in Cambodia, Vietnamese newcomers could easily obtain the necessary papers to Thailand upon payment of small bribes (Nguyen-vo, 1992:147).  Ea (1981:222) speculates that the majority of the 200,000-300,000 civilians who settled in Cambodia by the end of 1979 may have indeed crossed the border over to Thailand. Yet, the cumulative number of  Vietnamese land arrivals in Thai camps between 1976 and 1995 only amounts to about 43,000 (UNHCR, 1995b), a figure by far below Ea’s estimate of 200,000-300,000 Vietnamese settlers in Cambodia by the end of 1979.  Confirmation of the small number of Vietnamese land people in Thai refugee camps can also be found in several studies on Vietnamese refugees (Viviani, 1984; Hitchcox, 1990).  This suggests that most Vietnamese who settled in Cambodia did actually stay there.
	 To unravel the puzzle of Vietnamese emigration to Cambodia, consideration was also given to the possibility that Vietnamese settlers may have been enumerated in the 1989 Vietnam census.  The “Special Enumeration Groups,” a category enumerated separately in the 1989 census by the Ministries of Internal Affairs, Foreign Affairs, and National Defense (Banister, 1993:73-78), is believed to include Vietnamese cadres, technicians, experts and advisers in Cambodia who filled the spaces left empty by the massacres under Pol Pot and the exodus triggered by the Vietnamese invasion (Banister and Johnson, 1993:77).  As to the question of whether settlers were enumerated therein, the age and sex composition of the 1.04 million people in these special groups is disproportionately biased towards males ages 15-64, with a total ratio of six males to one female, and only a few tokens of children.  This leads one to discard this hypothesis, because a large portion of Vietnamese emigration to Cambodia may have consisted of entire family nuclei (Ea, 1981:222).
	Confirmation of the failure of the 1989 census to enumerate Vietnamese settlers to Cambodia is also found in census reports.  Acknowledging the absence of information on international migration in Vietnam 1989 census, the 1989 Census Steering Committee refers to international migrants as “…. the net movement of persons in the intercensal period who had left to seek residence in other countries, or who had moved into neighboring countries to farm or for some other purposes  [emphasis mine]” (Vietnam Central Census Steering Committee, 1990:40).  It is likely that this group refers to the Vietnamese settlers in Cambodia, who were counted in the 1979 census but not in the 1989 census. 

Estimating Vietnamese Emigration During the 1979-1989 Intercensal Period

Measuring Vietnamese Emigration from Vietnam’s 1979 and 1989 Census Data
Estimates of international migration can be obtained by the application of the life table forward and reverse survival methods to a pair of successive censuses (United Nations, 1970:26-27; Shryock and Siegel, 1976:359-360).   With this method, estimates of net migration by age groups can be calculated allowing for the components of population change, according to the formula: 

Ia - Ea = (P(1)a - sP(0)a-t), 

where Ia  - Ea  represent the difference between immigrants and emigrants, a is age at the end of the period, P(1)a , the population at this age in the second census, P(0)a-t the population t years younger at the first census, and s the intercensal survival rate for this age group. This formula covers all age cohorts except those born in the intercensal period.  For cohorts born in the intercensal period, the equivalent formula is: 

Ia - Ea = (P(1)a - sB),

where B represents intercensal births (Shryock and Siegel, 1976:357). 
	The application of the life table forward and backward survival procedures to Vietnam’s two successive census enumerations yields an estimate of intercensal net migration.  With the forward survival method, Vietnamese net migration M of persons in the cohort aged x to x+n at time t is equal to:

nMx  =   nPx+a (t+a) - [ nPx(t)  x  (nLx+a/nLx )]

	And, by reverse survival procedure, it is equal to:

nMx =  [ nPx+a(t+a) / (nLx+a/nLx)] - nPx(t) 

where
	nMx  = net Vietnamese migration over a years to the cohort aged x to x+n in first census and aged x+a to x+a+n at second census 
	a = length of the intercensal period in years
	x = age 
	n = cohort width
	t = date of first census 
	t+a = date of second census
	nPx  = Enumerated population in cohort aged x to x+n in first census 
	nPx+a = Enumerated population in cohort aged x+a to x+a+n in second census 
	nLx+a/nLx = a year survival ratios, that is the ratios of the size of the cohort aged x+a to  x+a+n to the size of the cohort aged x to x+n in the stationary population of the intercensal life table.

	The former procedure consists of applying life table survival ratios to the population enumerated in the first census to obtain an expected number of survivors in the following census. Subtraction of the survivors of the first census from the population enumerated in the second census yields an estimate of net migration M, or the number of Vietnamese who emigrated in the intercensal period and survived to the end of the period, and is equivalent to the assumption that all migration occurs just before the second census. This estimate overstates the population exposed to the risk of death during the intercensal period and is deficient as a count of emigrants by the number of deaths to the migrant cohorts during the intercensal period. 
	With the reverse survival procedure, application of reverse survival ratios to “young” the population enumerated in the second census, and subtraction of the population at the first census yields another estimate of net migration MN.  This estimate combines the number of Vietnamese persons who emigrated during the intercensal period and survived to the end of the period and those who died during the period, and is equivalent to the assumption that emigration occurred just after the first census (United Nations, 1970:26). 
	The average of the two estimates, MO , implies a more meaningful assumption regarding the timing of emigration than that implicit in either forward or reverse survival procedures.  This average will include migrant deaths with the implicit assumption that deaths and migration are evenly distributed over the intercensal period or that all migration occurs in the middle of the period (United Nations, 1970:26).  
	To allow for the effect of mortality of migrants dying during the intercensal period, life table survival ratios nLx+a/nLx are derived from Vietnam’s 1989 male and female life tables reported by Vietnam’s General Statistical Office (1991:116).  Because the interval between the dates of the two censuses, October 1, 1979 and April 1, 1989 is equivalent to 9.5-year, while only an abridged life table is available for 1989 in conventional 5-year age groups, the following steps are adopted to compute 9.5-year survival ratios:  (1) Coefficients based on the Sprague formula (Shryock and Siegel, 1976:555) are used to interpolate the series of 5Lx’s by single year of age; (2) a series of 1Lx+0.5 is constructed by taking the average of  1Lx  and  1Lx+1 on the assumption that mortality increases linearly within each pair of consecutive single years of age; (3) 9.5-year survival ratios are calculated by regrouping the values of 1Lx+0.5 thus obtained in 5-year age groups.  To make 1989 population counts comparable with 9.5-year survival rates, the last two steps are also applied to the 1989 census age distribution available in single year of age (Vietnam Central Census Steering Committee, 1994). 
	The estimation of deaths for the age cohorts born in the 9.5-year intercensal period  requires special treatment since these groups are exposed to the risk of death in Vietnam for less than 9.5 years.  Survival rates for the population under 5 and 5-9  during the intercensal period are computed respectively as [5q(5L0/5*l0)]1.25, or the probability of survival for 1.25 years for children aged 0-4 at the 1989 census and emigrated in the intercensal decade, and [q(l10/l5)], or the probability of survival for 2.5 years for children emigrated in the intercensal decade and aged 5-9 at the 1989 census..  The forward and reverse survival procedures are then applied in the same fashion as for the older age groups, with intercensal births providing the initial population for the first two age groups. 
	The main problem with intercensal survival procedures to estimate migration, is that  migration is estimated as a residual after all other components of change have been removed.  If the sources of error in the data are not known, and no prior adjustment is made, all errors and discrepancies in the data enter directly into the determination of the residual, and any changes due to errors are interpreted as net migration.  According to the authors of the 1989 census report, underenumeration in the 1989 census among males aged 15-24 is great, but its extent is not known (Vietnam General Statistical Office, 1991:19).  Table 2 shows estimates obtained from the intercensal projection method for males and females (detailed calculations of these procedures are presented in Appendix Table A1 and A2).  

[Table 2 about here]

	If these estimates truly represented the volume of net migration, there would have been about 1,240,000 male emigrants between ages 15 and 29, and about 440,000 female emigrants between ages 15 and 24, who left Vietnam between October 1, 1979 and April 1, 1989.  To these, one should add the relatively smaller numbers of exits estimated for younger and older age groups for a grand total of 1,947,000 male emigrants and 821,000 female emigrants and 2,768,000 emigrants for the two sexes combined.  These estimates are almost certainly too high for the period under consideration and are 1,000,000 people higher than the total count of 1,790,000 refugees reported by UNHCR  for the longer period from 1975 to 1995 (see footnote 2).  The suspicion is that they are a mixture of net migration and the net balance of errors in the basic data due to differential census coverage.  The estimates also imply some net immigration, as shown by the number of entries concentrated especially among  middle aged females, and to a smaller extent among middle aged males.  References to return migration during the period between the two censuses cannot be found anywhere, while repatriation of refugees by UNHCR began only after June 1989, following the 1989 census.  Differential enumeration between censuses and misreporting of age provide a more likely explanation for these results as undercounts selective of persons in certain age groups in 1979, especially of middle-aged persons (Banister 1993), would result in fewer survivors projected from 1979 to the date of the second census and a larger, possibly positive, residual when the projected population is subtracted from the population enumerated in 1989.  Similarly, age overstatement among males in 1979, because men older than 60 received higher benefits and were exempt from social work (Vietnam General Statistical Office, 1991:20), would result in evacuated age categories below age 60, hence in fewer survivors at these ages projected to the date of the second census and larger residuals.  Positive residuals would also be produced from age overstatement among females in 1989, because in rural areas women aged 45 and above were exempt from public service (Vietnam General Statistical Office, 1991:18-19).  A transfer of people from ages below 45 to older age groups would inflate the numbers enumerated in 1989 at these ages relative to the number of survivors projected from 1979.  Unfortunately, the absence of more detailed information on sources of errors in the data does not allow one to evaluate what proportion of “emigrants” estimated from Vietnam’s two census age distributions should be allocated to actual emigration and what proportion to differential census enumeration completeness. 
	 
Measuring Vietnamese Emigration from Immigration Data in the Censuses of the United States, Canada and Australia
The censuses of the US, Canada and Australia, with their questions on place of birth, are unique sources of consistent, up-to-date information on the immigrant stocks.  In fact, the number of Vietnamese-born persons enumerated in a census can be used to estimate immigration, because persons born in a different place from that in which they are enumerated are clearly migrants since they must have moved from elsewhere, presumably their place of birth, to the place of enumeration at some time (Zlotnik, 1987:936).  
The input data for the estimation of Vietnamese immigration  is provided by the censuses conducted at dates that are closest  to the two Vietnamese censuses of October 1, 1979 and April 1, 1989: for the US, the censuses of  April 1, 1980 and  April 1, 1990, for Canada the censuses of June 3, 1981 and June 4, 1991 and for Australia, the censuses of June 30, 1981 and June 30 1991 (See Figure 2).  In all three countries of resettlement, censuses taken prior to the 1980s do not enumerate Vietnamese-born persons as a separate category, and are therefore inadequate for providing information on Vietnamese emigration prior to 1980 (Barringer et al.,1993:37; Australia Bureau of Immigration and Population Research, 1994).

[Figure 2 about here]

	The forward and backward projection procedures applied earlier to Vietnam’s census counts to estimate emigration can be similarly applied to the Vietnam-born population enumerated in the censuses of the United States, Canada and Australia to obtain an estimate of Vietnamese intercensal immigration to these countries. 
	To allow for the effect of mortality of migrants dying during the intercensal period in the country of resettlement, life table survival ratios nLx+a/ nLx are derived from the intercensal life tables of the resettlement countries: for the US the 1985 life tables (National Center for Health Statistics, 1988), for Canada and Australia, the 1985 life tables (Keyfitz and Flieger, 1990). 
	Appendix Tables A3-A8 show the detailed calculations for males and females by country of resettlement.  A total of 333,898 Vietnamese (177,459 males and 156,439 females) immigrated to the US between the 1980 and 1990 censuses, 73,721 (36,961 males and 36,760 females) immigrated to Canada during the 1981-1991 intercensal period, and 83,011 (42,828  males and 40,183 females) immigrated to Australia in the 1981-1991 period. 
	The age and sex structure of Vietnam-born persons who immigrated to the US, Canada, and Australia during the intercensal periods is shown in Table 3.  It can be seen that Vietnamese immigrants are quite young, with the majority aged between 15 and 40, and little differences across country of resettlement.  This is not surprising, since migration is usually heavily concentrated among younger age groups (Gordon, 1989).  But contrary to expectations, the sex composition of Vietnamese-born enumerated in the 1990, and 1991 censuses of the US, Canada and Australia is fairly balanced. Only in the United States and Australia, is the excess of males over females more pronounced, especially between ages 15 and 34, while in Canada the sex ratio is balanced at almost all ages, with females exceeding males above age 30.

[Table 3 about here]
Some Difficulties of Measurement of Vietnamese Emigration from Data on Immigration to Countries of Resettlement
Estimation of Vietnamese emigration during the 1979-1989 intercensal period obtained solely from the estimated numbers of immigrants to resettlement countries requires several ad hoc procedures to make adjustments for the number of emigrants who are missed due to time lags between the dates of the Vietnamese censuses and the dates of the censuses of the countries of resettlement, and to unmeasured time lags between the date of departure from Vietnam and the date of resettlement to third countries.  In particular, the estimation of Vietnamese immigration to the US in the 1980-1990 period, and to Australia and Canada in the 1981-1991 period implies an exclusion of those who departed Vietnam between October 1, 1979, the date of the first Vietnam census, and April 1 1980, June 3, 1981, and June 30, 1981, the dates of the US, Canadian and Australian censuses (See Figure 2 above). 
	Moreover, the number of Vietnamese arrivals to the US is not an accurate representation of the number of departures from Vietnam during the same period.  While ODP applicants typically left Vietnam directly to one of the countries participating in the program, this is not so for boat and land people, who spent an unknown number of months in refugee camps in "first asylum" countries, before being accepted for resettlement in third countries.  While resettlement may have been relatively fast for selected groups claiming family reunification or employment ties to the US (Hitchcox, 1990:125), it may have been very slow for other less connected groups.  It is not uncommon among refugees in Southeast Asian camps to have spent more than two years in first asylum countries awaiting resettlement (Hitchcox, 1990:263).  Unmeasured time lags between the time refugees departed Vietnam and the time they reached resettlement countries complicate the estimation of Vietnam intercensal emigration in the following ways:
	a) Vietnamese emigrants who left Vietnam before October 1, 1979, the date of the first Vietnam census, but reached the US after April 1, 1980, the date of the US census will contribute to the estimated Vietnamese immigration to the US in the 1980 and 1990 intercensal period, but will have to be subtracted out because they were not enumerated in the 1979 census of Vietnam.  
	b) Vietnamese emigrants who left Vietnam after October 1, 1979, and reached the US before April 1, 1980, will not be included in the estimate of new Vietnamese immigration to the US in the 1980-1990 intercensal period because they were already enumerated in the US 1980 census. In the estimate of the volume of emigration from Vietnam, they will have to be added to the volume of Vietnamese immigration to the US in the 1980-1990 period.
	c) Vietnamese emigrants who left Vietnam before April 1989, the date of the second Vietnamese census, but entered the US after April 1, 1990 will not be enumerated in the US 1990 census, and therefore will not contribute to the estimate of Vietnamese immigration to the US between the two censuses of 1980 and 1990.  However, because they left Vietnam before the 1989 census, they must be included in the reconstruction of Vietnam’s intercensal emigration. 
	d) Vietnamese emigrants who left Vietnam after April 1989 but entered the US before the 1990 census will be included in the estimate of net intercensal immigration  but will have to be subtracted out because they were in Vietnam at the time of the 1989 census.    
	Similar problems are presented by the estimation of intercensal Vietnamese immigration to Canada, and Australia, only with different time lags between the dates of their respective censuses and the dates of the Vietnamese censuses.
	Figures 3 and 4 display monthly boat people movements over the periods encompassing the 1979 and 1989 Vietnam censuses.  These figures offer some indication of the sizes of groups a) through d), and of the potential impact of refugee movements on the estimation of Vietnam’s intercensal emigration. 
	From Figure 3, peak illegal emigration from Vietnam, at best represented by the number of boat people arriving in Southeast Asian camps, preceded the date of the 1979 census, the case of the group in (a).  However, by the time of the 1980 US census, a large number of refugees were still in camps, as the flow of arrivals to first asylum countries in 1979 was far too massive for Western countries to be able to absorb it at a fast pace.  This suggests that a substantial fraction of those who resettled to the US after April 1980, may have left Vietnam before October 1, 1979.  On the other hand, due to the slow pace of resettlement, the number of boat people who left Vietnam after October 1, 1979, but reached the US before April 1980 in (b), is probably comparatively small.

[Figure 3 about here]

	In the late 1980s, the number of  boat people arrivals to first asylum countries and resettlement departures to third countries was far smaller than the corresponding numbers in the late 1970-early 1980s, as the majority of those who left Vietnam during this period were ODP applicants.  Moreover, the probability of boat people being resettled in a third country was relatively low, as Vietnamese arriving to refugee camps in Southeast Asian countries and Hong Kong were likely to be classified as economic migrants and be denied resettlement.  

[Figure 4 about here]

	Figure 4 suggests that upon the establishment of the screening process in June 1989, the number of residents in the camps increased and stabilized around 110,000.  Some of these may have left Vietnam prior to the 1989 census, but, may have been denied resettlement in third countries.  For all we know, they may be among the 77,000 returnees to Vietnam, or the 38,000 still in camps in March 1996 (New York Times, 1996).  This indicates that the numbers of refugees who left Vietnam before the 1989 census but resettled to the US after the US 1990 census in (c), and of those who left after the 1989 census but reached the US before April 1, 1990 in (d), may be indeed small.  However, the difficulty to account for those who departed Vietnam prior to April 1989 but never made it to the US may jeopardize the accuracy of estimation of Vietnam’s intercensal emigration.
	Given the problems of measurement of Vietnamese emigration solely from information on immigration from pairs of census enumerations of the Vietnam-born population in the US, Canada and Australia, an alternative approach to estimating Vietnam’s intercensal emigration is proposed, one that combines data on the Vietnam-born population enumerated in the censuses of resettlement countries and UNHCR data on refugee movements.

A Comparison between Data on Vietnamese Immigration in the Censuses of  the Countries of Resettlement and UNHCR Data on Resettlement Departures 
To assess comparability  between resettlement departures from UNHCR records on refugee movements and immigrant entries to the US, Canada and Australia from the censuses of these countries, Table 4 compares the stocks of Vietnam-born persons who immigrated to the US, Canada and Australia estimated from the survival rate procedure based on census counts at destination, with the number of Vietnamese resettlements to these three countries recorded by UNHCR for the same years. 

[Table 4 about here]

	The difference is greatest for the United States, with the number of resettlements recorded by UNHCR exceeding the number estimated from US census data by 17 percent for the period between April 1 1980, and April 1, 1990.  Australia, exhibits a difference of  7  percent for the 1981-1991 period, while the counts are closest for Canada, with only a 2 percent difference for the same period.  
	How can the discrepancy for the US be explained?  Although census data on immigration are comprehensive with respect to all foreign-born persons in the US at the time of the census regardless of their legal status, and include aliens and citizens, persons having permanent residence status, and refugees (Warren and Passel, 1987:382), there are several reasons why US censuses may underenumerate Vietnam-born persons.  These include a tendency for those born abroad to report themselves as natives or, for Vietnamese-born of Chinese descent, to report themselves as Chinese-born, differential coverage between censuses, with better coverage of Vietnam-born persons in the 1980 census relative to the 1990 census, and differences between the census sample, on which data on the foreign-born population are based, and the 100 percent tabulations.  Similarly, UNHCR data on resettlement departures may be in turn inflated by an unknown proportion of double counts.  Refugees accepted for resettlement in the US were likely to spend about 20 weeks in Refugee Processing Centers (RPCs) in Indonesia and the Philippines, where they received language classes, cultural orientation and pre-employment training (Hitchcox, 1990:130-131).  This resettlement process may have produced some double counting as some refugees were counted for the first time as resettlement departures when they left “first asylum” camps for the RPCs, only to be counted again once they departed the RPCs for the US.  In recent years, UNHCR has devoted efforts to correct annual totals for double counting errors, with the results that recently published series are more accurate than earlier ones (personal communication with Ertan Corlulu, Resettlement Statistics, UNHCR, Geneva, 21 December 1995).  To minimize the impact of double counting errors on the total counts of resettlement departures between 1980 and 1990, only the most recent series were used here.  Moreover, despite the discrepancy between UNHCR counts and census counts, it is noteworthy that UNHCR counts of resettlement departures compare well with the total number of refugee arrivals to the US reported in Barringer et al. (1993:34) for the full 1980-1990 period (457,152 resettlement departures according to UNHCR data are only 5 percent less than 482,000 reported in Barringer et al.).  These counts represent the total number of physical arrivals of Vietnamese refugees to the US, including both non-immigrant and immigrant arrivals, and were estimated by these authors from unpublished records provided by the State Department, the Immigration and Naturalization Office, the Office of Refugee Resettlement, and its predecessor, the Indochina Refugee Program.  

Measuring Vietnamese Emigration from UNHCR Data on Refugee Movements, 1979-1989
Because UNHCR counts show a fair degree of consistency with the number of immigrants to the three major countries of resettlement estimated by the survival rate procedure, and, for the US, with those recorded by the independent data sources reported in Barringer et al. (1993), UNHCR data are regarded as a reliable source of information on the volume of emigration during Vietnam’s intercensal period.  In particular, the counts of boat and land arrivals to refugee camps in first asylum countries and direct ODP departures to countries of resettlement can be taken to reflect the number of departures from Vietnam minus an unknown proportion lost at sea. 
	Estimating the volume of Vietnamese emigration from UNHCR data on arrivals to refugee camps and ODP departures presents several advantages over the estimation of Vietnamese emigration from information from two successive census enumeration of Vietnam-born persons in the US, Canada and Australia.  First, it does not require any adjustment for different time lags between the date of the Vietnam censuses and the dates of the censuses of the three countries of resettlement, or for unmeasured time lags between the date of departure from Vietnam and the date of resettlement in the countries of final destination.  Second, the date of departure from Vietnam coincides with the date of arrivals to first asylum camps, as the journey time by boat generally required only three to four days (Viviani, 1984; Hitchcox, 1990).  Third, UNHCR data on arrivals to first asylum camps and ODP departures to resettlement countries enumerate all refugees regardless of their final destination, and include refugees who left Vietnam after the 1979 census and who, by the time of Vietnam 1989 census, were still awaiting resettlement in Southeast Asian camps.  
	From Table 5, a total of 559,736 refugees arrived to camps in “first asylum” countries or departed from Vietnam under the auspices of the ODP between October 10, 1979 and April 1, 1989.  This figure best reflects the volume of emigration from Vietnam in the 1979-1989 intercensal period, with the only exclusion of Vietnamese settlers in Cambodia.

[Table 5 about here]

	In order to estimate the number of  Vietnamese emigrants during the intercensal period who survived to the end of the period and who would have been counted in the 1989 census had they not departed Vietnam, the volume of the survivors of departures from Vietnam during Vietnam’s intercensal period, ought to be diminished by the proportion who died during this period while in refugee camps or in countries of resettlement.  
	As shown in footnote 11 of this paper,  M/MO is the ratio of the total number of Vietnamese-born persons immigrating to the country of resettlement during that country=s intercensal period and surviving to the end of the period to the combined number of Vietnamese-born enumerated in the censuses of the country of resettlement who entered during the intercensal period and survived to the end of the period and of those who died during the period.  This ratio is equivalent to the survival probability of Vietnamese immigrants who entered the US, Canada and Australia  during the intercensal period to the time of the census (1990 or 1991).  Its complement, 1 - M/MO , represents the probability of dying during the period, and was calculated for the US 1980-1990 intercensal period and for Canada and Australia 1981-1991 periods for each sex.  The left column of Table 6 shows the probability of dying for the US 1980-1990 period.  The right column shows the average of the probability of dying of Vietnamese immigrants to Canada and Australia for the 1981-1991 intercensal period.    

[Table 6 about here]

	Because the results obtained for the three countries of resettlement are very similar, the ratio M/MO for the US is employed to derive a single adjustment factor, on the assumption that the mortality experience of Vietnamese immigrants to the US is similar to that of their counterparts in Canada and Australia.  A factor equal to 0.985243 is finally derived by taking the weighted average of the US male and female survival probabilities M/MO raised to the 0.95th power to reflect 9.5-year survival for the length of Vietnam’s intercensal period.  This single factor is applied to the grand total of 559,736 arrivals to refugee camps and ODP departures from Table 4, to obtain the total number of emigrants who left Vietnam during the intercensal period and survived to the end of the period.  Thus, of the 559,736 persons who departed Vietnam between October 1, 1979 and April 1, 1989, 8,260 are estimated to have died and 551,476 survived.  This yields an average annual death rate of 1.55 per 1,000.  Such a low rate is not surprising, since the age structure of emigrants is quite young and death is a rare event at young adult ages.  This rate is also consistent with an average annual death rate of 1.59 per 1,000 for the 1980-1989 period in refugee camps, computed from UNHCR vital records published for refugee camps in Thailand (UNHCR, 1991). 
	In order to adjust one of the two Vietnamese census age distributions for the effects of net migration, it does not suffice to know the volume of emigration.  Knowledge of its age-specific intensity is also essential.  For the sake of computation efficiency, a single schedule is employed to apportion the 551,476 persons surviving to the end of Vietnam’s intercensal period to different ages. Because about 60 percent of Vietnamese refugees resettled in the US, and their age distribution is quite similar to the age distribution of their counterparts who emigrated to Canada and Australia, survivors are distributed according to the age and sex structure of Vietnamese-born enumerated in the 1990 census who immigrated to the US between 1980 and 1990, on the assumption that those who reached the US have the same age distribution of those who arrived to refugee camps. The estimate of the size and demographic structure of emigration from Vietnam between the 1979 and 1989 is shown in Table 7.  

[Table 7 about here]

	Not surprisingly, these estimates  reflect much lower levels of intercensal emigration than those derived from Vietnamese census data in Table 2, because they only incorporate the actual counts of refugees who left Vietnam after the 1979 census and were not there to be enumerated in the 1989 census, and are free from errors due to differential census enumeration completeness, and age misstatement.

CONCLUSIONS
The aftermath of the Vietnam war and the reunification of North and South Vietnam in 1975 opened the population of Vietnam to massive streams of outmigration.  The exodus of Vietnamese refugees started prior and immediately after the establishment of North Vietnamese control on Saigon in April 1975 and continued well into the 1990s.  About 90 percent of Vietnamese refugees have resettled in the United States, Canada and Australia.  Migratory flows to Cambodia during the decade of Vietnamese occupation 1979-1989 are also part of the story of Vietnamese emigration, although the cause of departure was of a different nature, since Vietnamese settlements in Cambodia were encouraged by the Vietnamese government whose objective was to reduce the overpopulation of the Red River delta in North Vietnam and redistribute people displaced in the South during the war (Ea, 1981:222). 
	The two modern censuses of Vietnam conducted in 1979 and 1989 represent the first official sources of data that allow the study of the Vietnamese population.  Yet, the absence of information on international migration in these data collection efforts complicates attempts aimed at obtaining reliable demographic estimates using two successive census enumerations.  This makes the measurement of Vietnamese emigration of even greater demographic significance.  
	This paper  attempts to measure Vietnamese intercensal emigration from a variety of data sources.   It first applies traditional intercensal projection techniques to Vietnam’s two census enumerations to estimate net migration as a residual after the other components of change, births and deaths, are accounted for.  The estimates of emigration derived in this fashion are heavily biased upward due to the inability to distinguish net migration from the net balance of errors in the data, most importantly differential census enumeration completeness, to which intercensal projection techniques are particularly sensitive.  
 	To remedy this problem and obtain more reliable estimates of the number of emigrants on an age and sex specific basis during Vietnam’s intercensal period, an alternative approach is illustrated.  This is based on a combination of counts of refugee movements documented by UNHCR and of data on Vietnamese immigration recorded in pairs of consecutive censuses of the US, Canada and Australia.  The former set of data provides an estimate of the volume of Vietnamese emigration during Vietnam’s intercensal period; the latter contributes the age-sex structure of Vietnamese persons who immigrated to the US, Canada and Australia in the period between censuses taken at dates that encompass or are very close to the dates of the Vietnamese censuses.  Although these new estimates of Vietnamese intercensal emigration are free from errors in the data that bias the estimates derived from the Vietnamese censuses, they are nonetheless not fully accurate.  The goal set forth in this paper is an ambitious one. The identification of all pieces of information on Vietnamese emigration since 1975 is a difficult task, mainly because the composition of migratory flows in the 1980s consisted of very diverse groups, and the documentation of these movements was complicated by the political, social and economic upheavals that took place in Vietnam in the aftermath of the Vietnam war.  A case in point is the emigration from Vietnam to Cambodia during the decade of Vietnamese occupation. 
Despite the meticulous accounting of Vietnamese emigration to receiver countries of Vietnamese refugees, that yielded a final estimate of 551,476 emigrants by age and sex who would have survived to be counted in the 1989 census had they not departed Vietnam, there remains an unknown amount of  “residual” emigration from Vietnam to Cambodia -- possibly about 200,000-300,000 persons -- who could not be accounted for by the estimation procedure.  The total absence of information on these flows makes it difficult to obtain an accurate measurement of intercensal emigration, and weakens the accuracy of the final results.  	 

FOOTNOTES