Introduction

The Manitoba Multigenerational Cohort (MMC) includes individuals born in Manitoba, Canada, from 1974 to 2020, and was developed to facilitate health and social research using family-based designs. The cohort was created using information from the Manitoba Health Insurance Registry, which includes all Manitoba residents registered for health coverage. Within the Registry, families are specified through unique family registration numbers (FRN) - using the Registration Number (REGNO) / (REGNO_CODE) variable; families are defined as all individuals who have the same FRN. FRNs can be used to link individuals with family members across four generations: great-grandparents, grandparents, parents, aunts, uncles, siblings and cousins. Updates to the MMC to include additional birth years can be facilitated given appropriate approvals.

Using an individual’s scrambled Personal Health Identification Number (PHIN), the MMC can be linked at the individual level to a wide range of health and social databases housed at the Manitoba Centre for Health Policy.

Methods

The methods section includes identifying the data source(s) necessary to operationalize this concept and the specification of familial relationships used in this concept.

Data Sources

The data source required to operationalize this concept is the Manitoba Health Insurance Registry.

Specification of Familial Relationships

Below, the specification of first-degree (parents, siblings), second-degree (grandparents, aunts/uncles), and third-degree (cousins, great-grandparents) relatives are described.

First Degree Relatives

• Parents: The first step is specifying male and female family head for the first registration each person has as a Child, Stepchild, or Incapacitated Child. For each individual born in Manitoba, we recorded the FRN for that first registration, and the date it started. The male registrant for that FRN was assumed to be the father, and the female registrant under the FRN was assumed to be the mother. In some cases (more frequently after the year 2000), the male or female registrant is blank, such as is the case with single parents or marriages not reported to MHSAL.
  
  
• Siblings: Siblings are defined as those sharing a female family head, for those having one specified, and male family head for those who do not. Individuals were first grouped by female family head because 98.1% of children had one, while male family head was only found for 59.9%. Single parents are more often female, and in the event of divorce the mother usually gets custody.
  
  These numbers reflect the situation around the time of birth, or first appearance in the registry. As each family progresses through its life cycle family heads may change, but the purpose of this was mainly to group children by family head at time of birth, not track the course of each child’s family head through childhood (although that too is possible). Full- and half-siblings can be distinguished provided both parents are specified. Twins can also be defined as siblings born into same FRN on the same day, although a definitive confirmation of twin or multiple births can only be done using birth records.

Second Degree Relatives

• Grandparents: Grandparents are defined as the male and female head of household listed for each parent specified in the first order relationships. Since FRNs were issued province-wide in 1970 and on a limited basis back to 1966, and individuals are listed as dependents under their parents’ FRN up to age 19 prior to 1992 (up to age 18 after that), we are only able to reliably specify grandparents of children whose parents were born in 1951 or later. Grandparents for some children whose parents were born as early as 1947 can be specified, but only for births after 1951 can the entire population be considered covered.
  
  
• Aunts: Aunts are defined as females sharing a female family head, for those having one identified, and male family head for those who do not with at least one parent identified in the first order relationships.
  
  
• Uncles: Uncles are defined as males sharing a female family head, for those having one identified, and male family head for those who do not with at least one parent identified in the first order relationships.

Third Degree Relatives

• Cousins: Cousins are defined as children who share the same FRN as an aunt or uncle assigned a head of family status.
  
  
• Great-Grandparents: Great-grandparents are defined as the male and female head of household listed for each grandparent identified in the second order relationships. Since we have FRNs province-wide going back to 1970 and on a limited basis back to 1966, and individuals are listed as dependents under their parents’ FRN up to age 19 (before 1992; up to age 18 starting in 1992), we will only be able to identify great-grandparents for children whose grandparents were born in 1951 or later. Great-grandparents for some children whose grandparents were born as early as 1947 can be specified, but only for births after 1951 can the entire population be considered covered.

Limitations / Cautions

• Children adopted at birth will have the same FRN as the adoptive parents, resulting in misclassification of biological relationships in the MCC. This is not expected to be significant at the population level. Birth records, available in the Repository, can be used to supplement the MCC and ensure only biological relationships are captured.
  
  
• A challenge arises from the increase in the prevalence of non-traditional family structures, including unmarried couples with children. While mothers can be identified for virtually all offspring, identifying fathers in the MCC is conditional on marriage or common-law status being reported for the father to be assigned the same FRN. Therefore, the ability to establish paternal-offspring linkage has been declining over time.
  
  
• Over time, linkages to biological mothers improved (from 93.3% in 1974 to 99.1% in 2019) and linkages to biological fathers worsened (from 85.5% in 1974 to 39.2% in 2019).