Concept: Birth Cohort Registry - Methodology

Concept Description

Last Updated: 2023-04-03


Birth Cohort Registry


Data Sources

Steps in the Development of the Birth Cohort

1. Link Database Records

2. Distinguish Among Family Members

3. Select Additional Database Linkages

4. Select Birth Years

Issues Selecting Birth Years for a Cohort

    The following are some of the issues encountered by MCHP regarding data availability for certain databases that will affect the selection of birth years for a cohort. (Personal Communication with Leslie Roos, July 12, 2011).

    • Dates
      • Health data is recorded by fiscal years, whereas education data is recorded by calendar years. For ease of analysis, it is suggested that April 1 of the desired start year is used at the start date.

    • Education Data
      • Education data became available in the 1995 academic year (school year 1995/1996) (birth cohort of 1978); however, some of the education variables are incomplete for the 1978 cohort. The quality and completeness of the education data improves with time as the more recent years capture more standardized test scores than the earlier ones. Data from 1979 and on should generally be used.
      • Standardized test scores were not available for the 1999 academic year (school year 1999/2000), thus in the selection of birth cohorts, 1983 should be excluded. (Information from Charles Burchill, August 5, 2011)

    • ICD Codes
      • ICD coding has changed over time: ICDA-8 was used until April 1, 1979, when ICD-9-CM began being used. For ease of analysis, it is suggested that April 1, 1979 be used as the start date.
      • Use of ICD-10-CA began April 1, 2004. The "ACG/ADG system provides a way to automatically cross-walk across this transition" (email from Les, Aug. 13, 2009).

    • Study Files
      • Ideally, variables of interest would be available for 18 years, allowing us to follow the cohort from birth to adulthood. In reality, not all variables are available for the desired 18 years. For example, Child and Family Services Information System (CFSIS) and Employment and Income Assisitance (EIA) (also known as Social Allowances Management Information Network (SAMIN)) variables have only been available since 1992, and 1995, respectively (more information can be found in the database summaries provided in the respective links below ). These are important variables associated with child health and development, and thus often need to be included in the analysis,

      • The CFS data is most complete in the years 1995-2005. Thus, when birth cohorts are used, each cohort will differ in the number of years for which records are most complete.

        Two approaches to analyzing such information have been tried:
        1. Variable age range
          • all the years available for each individual birth cohort (up to each child's 18th birthday) are used
        2. Fixed age range
          • coverage at fixed ages (13th to 18th birthday) for each birth cohort is used

        "The latter approach 'loses' some children who receive aid from CFS but makes sure that each child is categorized using the same number of years of information. Since these (and other) approaches can be tried with little more work than that associated with using just one, sensitivity testing is especially appropriate here." (This information is from an email from Leslie Roos, Feb. 26, 2009.)

    • Place of Residence
      • The definition of residential area boundaries in Manitoba has changed over time, making it difficult to evaluate social mobility up/downwards over time. MCHP has a cross-walk between postal codes and the 1986 census which enables better comparison of individuals across space and time. The 1981 census can be used with just a few corrections (please see Documentation of Census and Postal Code Data for more information ( internal access only ).

5. Select Inclusion and Exclusion Criteria of Subjects

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