Max Rady College of Medicine

Concept: Number of Children

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Concept Description

Last Updated: 2024-03-12


    concept/Social Determinants of Health-SDOH-Digital Library-Image.jpg Number of children has been defined at the Manitoba Centre for Health Policy (MCHP) as the number of children aged 0-18 years who, as best determined from the data, live together in one household.

    Number of Children has been measured in two different ways:

    1. Counting the number of children born to a mother; and
    2. Counting the number of children with the same Registration Number (REGNO) / (REGNO_CODE) at the same date(s).

Definition and additional information: Significance

    Empirical literature has suggested a negative relationship between family size and child well-being (usually measured by educational attainment). (Black, Devereux, and Salvanes (2005) suggest that these findings are based on the preconception that greater family size may negatively affect a child's outcomes due to resource dilution or a lower average maturity level in the household. They examined the affects of family size and birth order on the educational attainment of children and "found a negative correlation between family size and children's education, but when [they included] indicators for birth order or [used] twin births as an instrument, family size effects [were] negligible" (Black, Devereux, and Salvanes, 2005, p. 669) .

    There may be different operational definitions of the number of children in a family, depending on the timing of the measurement and how a family and a child are defined. Here, the focus is on how the number of children has been measured in MCHP-related research.


    Method 1: Counting the Number of Children Born to a Mother
    First, the cohort of children or mothers for which family size will be calculated must be identified (e.g., children aged 0-18 on April 1, 2001). This method is a two-step process: mother and baby records must first be matched together and then the number of children born to that mother can be calculated.

    a) Matching Mother and Baby Records

    Determining the number of children born to a mother requires matching the baby's birth records to the mother's records. In this step of the analyses, duplicate baby Personal Health Identification Numbers (encrypted PHINs; a unique numeric identifier assigned by Manitoba Health to every person registered for health insurance in Manitoba) were removed.

    Note: the mothers' files were not limited by date of admission to ensure that mothers admitted a longer period before the baby was born would be included in analyses.

    b) Calculating the Number of Children

    A mother/baby linkage file and the Manitoba Health Insurance Registry Data can be used to calculate the number of children. Mother/baby records going back to 1970 can be checked. Children's ages may vary widely (e.g., children born as early as 1951 and as late as the most recent update). The Manitoba Health Insurance Registry (MHIR) data begins with families as of 1970 (and will thus include children born in 1951 and later). The number of children born to each mother were counted, excluding children who:

    • were born when the mother was less than 12 years of age (assumed to be an error)
    • did not have a valid numeric encrypted PHIN (assuming these children probably did not survive birth).

    When analyzing the birth records, some children may be linked to more than one mother's family. A suggested solution is to first use the birth mother of the child in the analyses. If no birth mother can be found on the baby's record, the female parent indicated on the baby's record from the Registry can be used.

    When attempting to inform population projections, it may make sense to count all of the children born (and then delete those who have died) to mothers in a given area whether or not they are still children. Looking at the current number of children under 19 will only give planners a sense of potential differences across SES (socio-economic status) groups.

    Method 2: Counting the Number of Children With the Same Registration Number (REGNO) at the Same Date(s)

    This method simply involves counting the number of children who have the same REGNO number on their Manitoba Health Insurance Registry file at the same date.

    a) Description of REGNO Families

    Most 18-year-olds are classified as a family head because children are issued their own REGNO at age 18. For some analyses, 18-year-olds still classified as children can be counted as children. The family head can change over time within an ongoing registration "family".

    Prior to April 1992, dependent children automatically received their own registration number (as a family head) on the first day of the first calendar month following their 19th birthday. Since April 1992, dependent children automatically receive their own registration number (as a family head) on the first day of the first calendar month following their 18th birthday. The new registration card is mailed to the most recent known address of the parent/guardian/family head of their previous registration. Thus, the only contact required between Manitoba Health and the two REGNO families is the delivery of the new cards.

    The year 1992 was selected because that was when Manitoba Health originally set out the specifics for the Drug Program Information Network (DPIN); which is based on PHINs even though the original deductible was based on family head age (i.e., via REGNO)]. The change was also made because 18 years is the age of majority in Manitoba, not 19 years of age.

    If the card (and the new version of the original registration card to the family head) is returned, Manitoba Health will investigate and try to locate either or both family heads. If they cannot be found, both registrations can be cancelled. Persons taking up residence elsewhere in Canada and registering there will be reported by that province and coverage will be transferred to the new jurisdiction on the first day of the third calendar month following the date of the move (this shows up as a cancellation in Manitoba).

    In rare cases, dependent children (natural or step) may become dependent adults under the original registration and thus keep the original REGNO.

    A parent may notify Manitoba Health of a previously unreported death or other ineligibility of the dependent child. Manitoba Health may then decide to rescind the "new" registration of the dependent child before it takes effect.

    In the event of a cancellation of the most recent family head, REGNOs can be reassigned two or more years after the cancellation.

    b) Exclusions and Exceptions

    All persons under the age of 18 are children but are not necessarily dependents in a REGNO. Anyone, including children, may request a private health registration card (and REGNO) and, therefore, would appear as a separate family head. As a result, children aged 18 or less who are classified as the family head, spouse or common-law spouse of the family head were excluded from analyses. Most of these children are the sole members of a REGNO family or are aged 16-18 and actually the parents in a family.


    Some newborns or new registrant dependants may have been entered more than once in the same family/registration. This has been seen in a few cases involving multiple births (i.e., twins). For further details, see Family Size - Internal Documentation (internal access only) .

Related concepts 

Related terms 


  • Black SE, Devereux PJ, Salvanes KG. The more the merrier? The effect of family size and birth order on children's education. Q J Econ 2005;120(2):669-700.(View)
  • Oreopoulos P, Stabile M, Walld R, Roos LL. Short, medium, and long term consequences of poor infant health: An analysis using siblings and twins. J Hum Resour 2008;43(1):88-138. [Abstract] (View)
  • Statistics Canada. "Family size (for census family).” Definitions, data sources and methods. September 9, 2021. (Published on the Statistics Canada website: - accessed on February 20, 2024) . [Summary] (View)


  • cohort
  • family
  • family structure
  • marital status
  • socioeconomic status

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Manitoba Centre for Health Policy
Community Health Sciences, Max Rady College of Medicine,
Rady Faculty of Health Sciences,
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