Concept: Household Income from Census Information - Historical

Introduction

The Canadian Census, conducted every 5 years by Statistics Canada, provides The Manitoba Centre for Health Policy (MCHP) with many areas of information on Canadians, including income. MCHP has census records from 1976; however not all census years collected income data. The census reports income by geographical areas that are defined by Statistics Canada (enumeration areas (EAs) from 1986; dissemination areas (DAs) from 2001). Because MCHP specifies place of residence by postal code, income data reported by EA or DA must be applied to postal code areas in order to analyze neighbourhood household income. This concept discusses steps taken by MCHP to specify household income from censuses by postal code. SAS code for the steps is also provided ( internal access only ).

Methods

The following is a description of methods used at MCHP to specify household income by postal codes using the 1976-1986 censuses. This information is based on a detailed technical report by Brett Hiebert, Documentation of Census and Postal Code Data ( internal access only ).

Summary

The work to determine the average household income at the postal code level for years 1976 and 1981 involved obtaining data from several sources and applying the data to census EAs and eventually postal codes. The earliest postal code conversion file (PCCF) available is in 1986. The PCCF describes the relationship between census EAs and postal codes. This allows household income from the 1986 census to be directly applied to postal codes. EA conversion files from the 1976 census and the 1981 census were applied to the 1986 census file so that the 1986 PCCF file could assign postal codes to the respective EAs in prior census years. Since income at the EA level was available on the 1981 census, the assignment to postal codes went relatively smoothly with minimal error; however the 1976 census did not record income variables.

Census tract incomes for Winnipeg were obtained from 1971 and 1981 census data to obtain an average income increase for approximately 100 census metropolitan areas (CMAs) in Winnipeg. These income inflation values were then applied to the corresponding EAs, and eventually Winnipeg postal codes for 1976. Rural incomes were obtained using similar 1971 and 1981 census data however the only available census level to obtain income inflation values were at the electoral district level. The final files contained our best estimates of average household income by postal code for census years 1976 and 1981.

Population wide data on neighborhood household income at the level of census dissemination area or enumeration area is readily available from the 1981 census onwards and the relevant Postal Code Conversion Files are available through Statistics Canada. The 1986 Postal Code Conversion Files have been adapted in Manitoba to work with 1976 and 1971 postal codes. The 1981 census information on household income could be worked with directly with minimal error. We imputed 1976 neighborhood household income for each individual at the census enumeration area while accounting for inflation, changes in census areas, and economic growth statistics for various areas of Manitoba.

Data Sources

Eight data sources from the Manitoba Population Research Data Repository (Repository) are needed to determine average household income at the postal code level for 1976 and 1981, including:


• 1976 Census file
  • Provides information obtained from the 1976 Canadian Census
  
  
• 1981 Census file
  • Provides information obtained from the 1981 Canadian Census
  
  
• Postal Code Conversion File (PCCF) of the 1986 census
  • Provides a bridge between the small geographical areas (e.g. EA) defined by Statistics Canada and postal codes.
  • This is the earliest PCCF available.
  
  
• Census Conversion files between the 1976 and 1981 censuses, and between the 1981 and 1986 censuses
  • Provides information on changes in geographical area identifies between census years
  
  
• Population registry files from 1976 and 1981
  • Provides information on the population of Manitoba (including postal codes)
  
  
• Income by Census Tract file of the 1971 and 1981 censuses
  • Provides a list of average income by census tract for the 1971 and 1981 census years
  • Allows for a yearly income inflator to be calculated between 1971 and 1981 for each tract

Description of Steps

The following is a brief description of the steps that have been performed on the above files to determine household incomes for postal code areas from the 1976-1986 censuses.


1. Created compatibility of geographic area identifiers between data files

   Geographic area identifiers (Federal Enumeration Area (FEDEA) in the 1986 PCCF ; GEO_ID in the census conversion files ) were made compatible by adding 46,000,000 to the FEDEA variable.

2. Selected Manitoba EA codes

   Only Manitoba EA codes (those beginning with 46) were selected from the 1981-1986 census conversion file.

3. Compared EAs across data files
   

   The 1986 EAs were compared across the 1986 PCCF and the 1981-1986 census conversion file . It was found that all 1986 EAs matched between these two files.

4. Merged PCCF with Census Conversion file to create "File A"

   Multiple values in the 1986 PCCF and the 1981-1986 census conversion file were merged to create a new file that included postal code listings, the 1986 EAs, the 1981 EAs, "birth dates" of postal codes and "retirement dates" of postal codes. (For the purpose of this concept, this file is designated with the arbitrary name of "File A". The steps 5 through 9 involve further alterations of "File A".)

5. Merged "File A" with 1981 Census
   

   The 1981 EAs are used to merge "File A" with the 1981 census file to obtain information on income and the number of reporting households in the 1981 census.

6. Calculated weighted average of household income for postal code areas, if necessary
   

   For cases in which the postal code was found in multiple EAs, a weighted average of household income was calculated to estimate the income in postal code areas. This step was not necessary if the postal code was not found in more than one EA.
   
   SAS code for steps 1 to 6 can be found below ( Census Linkage - 1981 ).

7. Merged "File A" with 1981 Population File to evaluate matching of 1981 postal codes
   

   "File A" was merged with the 1981 population file to determine how well postal codes in the 1986 PCCF matched those in the 1981 population file .
   
   SAS code for step 7 can be found below ( Checking 1981 Postal Codes ).

8. Merged "File A" with 1976 census to identify 1976 EAs

   The 1976 EAs were identified from 1981 EAs by merging the 1976 census to "File A", through the 1976-1981 census conversion file.
   
   SAS code for step 8 can be found below ( Census Linkage - 1976 ).

9. Merged "File A" with 1976 Population File to evaluate matching of 1976 postal codes

   These postal codes were linked to the 1976 population file to evaluate how well the 1986 postal codes matched the 1976 postal codes.
   
   SAS code for step 9 can be found below ( Checking 1976 Postal Codes ).

10. Developed a yearly income inflator

    Income by census tract (CT) data from Statistics Canada was used to create a yearly income inflator that could be used to estimate income for years between 1971 and 1981, inclusive.

11. Matched EAs with CTs to create "File B"

    The income inflator from step 10 was merged with the income by census tract file to match EAs with CTs. An income inflator and EA code was specified for each Winnipeg EA that allowed for linkage to MCHP files.
    
    SAS code for step 11 can be found below ( Census Tract to Enumeration Area - 1981 Census ; Enumeration Area Income - 1971 and 1981 Census ).

12. Linked "File A" from step 9 with "File B" from step 11 to yield income by postal code

    1981 EA codes were used to link "File A" from step 9 to "File B" from step 11. This linkage produced 1976 income values by postal code.

13. Assigned income values to remaining postal codes

    Postal codes that were not found in both "File A" and "File B" were assigned an income value based on average inflation between 1971 and 1981 electoral districts.
    
    SAS code for steps 12 and 13 can be found below ( internal access only - Obtaining EA7681 Income ).

Cautions

In the 1986 PCCF, September 26, 1982 was the earliest "birth date" and "retirement date" for postal codes; therefore we are unaware if a postal code contained within the 1986 PCCF was created or eliminated between 1976 and 1981.