Chapter 7
Interprovincial migration

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7.1 Data sources and relevant concepts
7.2 Estimates of Interprovincial migration, Canada, provinces and territories

Movements of persons, who change their usual place of residence, crossing provincial/territorial boundaries, are classified as interprovincial migration. Intraprovincial migration (or subprovincial migration) also involves a change in usual place of residence, but these movements occur within the same province or territory. The term "internal migration" may refer to either interprovincial migration or intraprovincial migration, or both. This chapter focuses on the interprovincial migration component. For information on intraprovincial migration, see Chapter 8 on subprovincial estimates of population.

As is the case for emigration, there is no provision for recording interprovincial migration in Canada. Consequently, this component of demographic growth has to be estimated using administrative data. The methods used to prepare estimates of interprovincial migration will be discussed in this chapter.

7.1 Data sources and relevant concepts

Canada Revenue Agency (CRA) provides Statistics Canada with data from the Canada Child Tax Benefit (CCTB) program and personal income tax returns, which are used to estimate interprovincial migration. Preliminary¹ estimates by month are derived quarterly from CCTB data, while final estimates are derived annually from the T1 Family File (T1FF)².

Since 1976, personal income tax records have become the official data source for final interprovincial migration estimates. The population covered by tax data is more comprehensive than that of the CCTB; in general, interprovincial migration estimates based on tax data are considered to be of higher quality than those produced using data from the CCTB. However, tax data are not timely enough for use in preliminary estimates. Statistics Canada receives tax data only after annual processing, compared to CCTB data which are available on a monthly basis.

7.2 Estimates of interprovincial migration, Canada, provinces and territories

7.2.1 Final estimates of interprovincial migration

Final estimates of interprovincial migration are produced using personal income tax data. By comparing the place of residence at the time of filing, it is possible to identify for those persons who file returns for two consecutive years, those who move, their place of origin and their destination. The development of migration data involves four main steps³:

1. geo-coding of tax records;
2. estimation of non-filing dependants of tax filers, by age groups and gender;
3. identification of migrant tax filers by age group and gender;
4. adjustment for the population not covered by the T1FF.

The four steps of the estimation methodology are described below.

Step 1—geo-coding

The migration data developed from the taxation records are estimates of migration flows between census divisions (CDs) or census metropolitan areas (CMAs). The geographic coding of CDs and CMAs on the tax records is done primarily on the basis of the postal code, which is a part of the mailing address. Tax records also contain a "locality code" assigned by Revenue Canada based on place name, which is a combination of Standard Geographic Classification (SGC) codes used by the census. About 99% of all tax records are filed with a postal code, or are assigned one, based on the filer's address by matching the address to a file similar to the Postal Code Directory from Canada Post. As the tax return is usually submitted several months after the end of the tax year, the postal codes correspond to those existing in the spring of the year following the tax year.

Step 2—estimation of dependants

Since the tax records source file has no direct information on the number and characteristics of non-filing dependants, this information must be imputed. Following the 1988 tax reforms, the estimation of tax filers' dependants is obtained from the T1FF. The family system creates families by linking all filing family members together, using spousal social insurance numbers, marital status, and matched addresses. This system imputes a non-filing spouse whenever a filer has declared himself/herself married but was not linked to a filing spouse. Children are imputed based on CCTB data, which carry the social insurance number of the parent receiving the benefit. Newborns are added to tax filer records from Statistics Canada's vital statistics birth database, and in addition a historical file of imputed children is created from the previous year's tax file⁴.

The family data from the tax file are then used to create a file of individual tax filers for the migration system. The migration file contains information for each tax filer and assigns dependants to each tax filer based on the number of filers in the family, and the number of dependants. If only one parent in the family has filed a tax return, then all dependants, including the spouse, if one exists, are added to the tax filer's record. If both parents filed tax returns, and their family record contained dependant children, then each tax filer would receive half the count of dependants.

If not already present, the age of the dependant spouse is estimated in the family system. The age of imputed children is provided (date of birth) on CCTB records, birth files from vital statistics, and from the Historical Family File. The family system does not impute gender for non-filing children. The gender for each dependant child is assigned a male/female ratio based on information from the most recent census.

Step 3—identifying migrant tax filers

After assigning the geography codes and non-filing dependants to each tax filer, records for two consecutive years are matched by social insurance number. Only records of tax filers who are present in both years are retained. Migrant tax filers are identified by comparing current and previous geography codes (CDs or CMAs). Thus, it is only possible to determine migrant status for those who file in two consecutive years. The identification of migrants is based on their address at the time of filing, and thus the migration period is not precisely one year, but it is assumed to be close. The assumed reference period is around April to April, of the year following each tax year. However, in the Demographic Estimates Program the given estimates cover the period from July to June. Tax filers' non-filing dependants are assumed to have the same migration behaviour as that of the filers to whom they are assigned.

Step 4—coverage adjustment factor

The final step in the estimation process is an adjustment for coverage, done at the CD/CMA level for gender and specific age groups. This adjustment is required to estimate those migrants who did not file two consecutive personal income tax returns, which involves the calculation of coverage adjustment factors (or inflation factors). Population estimates by CD/CMA are used as the denominator to the same population for whom two consecutive income tax returns could be linked to create coverage ratios.

For migration estimates prior and up to 2000/2001, provincial adjustment ratios were substituted in place of the CD/CMA ratio in the few cases where coverage was abnormally high or low (outlier values in the coverage ratios). Beginning with 2001/2002 migration data, high and low coverage cases were identified with a different methodology and a Canadian adjustment ratio was used in place of the CD/CMA ratio for these outlier coverage ratios. After a review and analysis of these methods, it was determined that cases where the coverage ratios were deemed outlier, represented small domains having little impact on the measure of migration, moreover, it was known that replacing the coverage ratios with a national ratio had the effect of reducing the true measure of migration flows. Consequently, beginning in 2006/2007, the identification and treatment of high and low coverage cases was discontinued and the coverage was simply adjusted to the Demography Division data at the CD level by age and sex group.The same adjustment is also done for CMAs.

The adjustment ratios are applied to the counts of interprovincial out-migrants derived in Step 3 to obtain an estimate of total migration. The basic assumption is that the population not covered by the taxation system has the same rate of migration as those for whom it can be measured.

7.2.2 Preliminary estimates of interprovincial migration

Preliminary estimates of migration between provinces and territories are produced using CCTB data, along with data from personal income tax records, processed by Income Statistics Division. Because the CCTB program is not universal and does not provide direct information on the number of adult migrants, this estimation requires three adjustment factors to derive the complete estimate of interprovincial migration:

1. the program's partial coverage (i.e., persons who do not apply to the CCTB program or who are not eligible);
2. the differential propensity to migrate between children who are receiving benefits from the CCTB and children who are not;
3. the differential propensity to migrate of adults as compared to that of children.

Each of these adjustment factors makes use of data from CCTB and T1FF. The estimation methods for child and adult interprovincial migration rates are described in the next section.

Interprovincial migrant children

Since income tax returns are annual and not available at the time when preliminary estimates are produced, the estimation of preliminary interprovincial migration is based on CCTB administrative files, which provide counts of child migrants (aged 0 to 17) receiving benefits under the program on a monthly basis. The data provide monthly information on the changes of usual residence involving provincial or territorial boundaries of CCTB-registered children receiving benefits and the total number of children registered for the CCTB program by province and territory. As mentioned, the CCTB program is not universal and targets families with lower income or families with a larger number of dependent children; therefore the data are incomplete in terms of estimation of total child migrants and require adjustments.

The estimation of interprovincial migrant children involves two adjustment factors. The first factor reflects the CCTB program's coverage: the ratio of the number of children as estimated by Demography Division, to the number of children receiving benefits from the CCTB program, for each month and province and territory. The second factor, which corrects for any biases resulting from the differential propensity to migrate between children who are receiving benefits from the CCTB and children who are not, is obtained by comparing the interprovincial out-migration rates of children receiving the CCTB with the out-migration rates for all children (aged 0 to 17). The adjustment factor is calculated for each province and territory and is based on the two last available years of T1FF.⁵

The formula to estimate children migrating between provinces/territories is as follows:

Equation 7.1:

Description

where

  =  number of migrant children from province/territory of origin j to destination province/territory k;

  =  interprovincial migration of children according to CCTB data by province/territory of origin j to destination province/territory k;

=  coverage rate of CCTB program for province/territory of origin j;

_jG =  adjustment factor for differential migration propensity among children for province/territory of origin j.

The equation above includes the adjustments for incomplete coverage of CCTB-children who receive benefits (Equation 7.2) and for the differences in the propensities of this group to migrate as compared to all children (Equation 7.3).

The coverage rates are calculated on a monthly basis as follows:

For each province and territory:

Equation 7.2:

Description

 

where

  =  coverage rate of CCTB program for each province/territory j;

=  number of children aged 0 to 17 years registered for the CCTB program in province/territory j:

=  population estimated by Demography Division of children aged 0 to 17 years in province/territory j.

The differential migration propensity is based on a set of _jG factors. Using tax data, the _jG factors are obtained by dividing the interprovincial out-migration rates for all children by the out-migration rates of children receiving benefits from the CCTB program, as follows:

For each province and territory:

Equation 7.3:

Description

Description

   

where

_jG  =  adjustment factor for the differential migration propensity by province/territory of origin j;

_jRate_Tax_IM^0-17 = interprovincial out-migration rate of all children from province/territory of origin j, according to income tax data;

 _jRate_CCTB_IM^0-17  = interprovincial out-migration rate of CCTB-registered children from province/territory of origin j, as modeled from tax data (T1FF);

^Tax _jIM^0-17 = number of total out-migrant children from province/territory of origin j, according to income tax data;

 ^Tax_jP^0-17 = estimate of children in province/territory j based on income tax files;

^CCTB _jIM^0-17 = number of out-migrant children eligible for CCTB benefits from province/territory j, according to tax data;

^CCTB _jP^0-17 = CCTB-registered children in the population of the income tax files provided by T1FF, by province/territory j.

The _jG factor will equal one if the migration rate of children receiving CCTB benefits and the migration rate of all children are identical. A value of _jG that is greater (or less) than one indicates that the propensity to migrate of children receiving CCTB benefits is less (or greater) than that of all children.

Interprovincial migrant adults

The third factor in adjusting the estimates from the CCTB data is used to calculate the number of adult migrants. Estimates for adults migrating between provincial/territorial boundaries are obtained through the calculation of modeled migration ratios of adults to children referred to as F factors. The F factors, calculated from the most recent tax data, are equal to the ratio of the adult migration rate to the child migration rate, by province/territory of origin and destination province/territory, as follows:

For each province and territory of origin and destination:

Equation 7.4:

Description

Description

   

where

= average adult estimation factor calculated over three migration periods by province/territory of origin j and province/territory of destination k;

= average adult migration rate over three migration periods by province/territory of origin j and province/territory of destination k;

= average child migration rate over three migration periods by province/territory of origin j and province/territory of destination k;

 = adult migration by province/territory of origin j and province/territory of destination k, according to income tax data for periods (t-3, t-2), (t-2, t-1), (t-1, t);

= adult population estimated by Demography Division for province/territory of origin j at time (t-2);

= child migration by province/territory of origin j and province/territory of destination k, according to income tax data for periods (t-3, t-2), (t-2, t-1), (t-1, t);

= child population estimated by Demography Division for province/territory of origin j at time (t-2).

The _j,kF factors once applied to the child migration rates (based on adjusted CCTB data) produces estimates of adult inter-provincial/territorial migration rates. These are then multiplied by the provincial/territorial populations to obtain estimates of the number of adults migrating between provincial/territorial borders, as follows:

For each province and territory:

Equation 7.5:

Description

where

= estimated number of adults migrating from province/territory of origin j to province/territory of destination k;

= migration rate of children (estimates by province/territory of origin j and province/territory of destination k based on the adjusted CCTB data);

  = population estimate of adults at province/territory of origin j at the beginning of the period;

= average adult estimation factor calculated over three migration periods by province/territory of origin j and province/territory of destination k.

Finally, after the estimates of the total number of interprovincial migrant children and adults have been separately calculated by province/territory of origin and destination, interprovincial migration estimates are obtained by adding the interprovincial migrants of children and adults, as follows:

For each province and territory:

Equation 7.6:

Description

Interprovincial migrant population by age and sex

Final interprovincial migration estimates are derived from the T1FF file consisted solely by five broad age groups (under 18, 18 to 24, 25 to 44, 45 to 64, and 65 years and over) by sex, as well as origin and destination province/territory.

To estimate the number of interprovincial migrants by age and sex, the following steps are followed:

1. calculate migration by sex and five-year age group cohorts using the number of migrants by province of origin and destination obtained from the one-year ago mobility question from the most recent census;
2. split the migration cohort into single-year of age using Sprague's multipliers;
3. calculate a percentage distribution by single years of age for each broad age-sex group (under 18, 18 to 24, 25 to 44, 45 to 64, and 65 years and over), using the data obtained in step (ii);
4. apply the distribution obtained in step (iii) (which remains constant for the five-year postcensal estimates) to the interprovincial migration estimates by broad age group and sex, in order to disaggregate them into a distribution by single-year of age;
5. Finally, to eliminate inconsistencies from one age to another, the number of migrants by single-year of age, is aggregated by five-year age groups, to which Sprague's multipliers are again applied.

To produce the preliminary interprovincial migration estimates by age and sex at provincial/territorial level, the most recent age and sex distribution of final estimates is applied.

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Notes:

1. Unless otherwise noted, the term preliminary includes both preliminary and updated estimates.
2. The T1 Family File (T1FF) is derived from the Canada Revenue Agency (CRA) T1 file by Income Statistics Division of Statistics Canada.
3. For a detailed description of the methodology, see Statistics Canada 2010d.
4. The Historical Family File, updated annually by Income Statistics Division of Statistics Canada, consists of information of known family relationships obtained from tax returns.
5. See Step 3, Section 7.2.1, for a description of the process to identify interprovincial migrants.