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Population aggregates at CBG and CT not matching (for ACS and Decennial Year as well)

Madalsa Singh
over 2 years ago

Hi,

I'm using population estimates at census tracts and census block group level for race and ethnicity. Despite coming from the same tables, why don't the aggregate totals not match at census tract and census block group level? I have tried this with ACS 2015-2019 as well as latest 2020 data (taken from NHGIS). Basically, I'm extracting this data from the same table at different geographic level but curious to know what the source of discrepancy *within* same dataset could be to find different totals?

For instance, 

  • ACS 2015-2019
    • The sum of population at Census Tract level is 328.016242 and latinos are 16.558998 (in millions).
    • The sum of population at Census Block Group Level  is 322.538633 and sum of latinos are 30.969603 (in millions).
  • Census 2020 
    • The sum of population at Census Tract level is 329.82495 and latino total sum is 62.57364
    • The sum of population at Census Block Group Level is 324.412244 and latino population 59.15539
Parents
  • over 2 years ago

    I just got data for the entire US and Puerto Rico from NHGIS for the counts and levels you identified. My totals are different from the ones you derived, and I find no inconsistencies between the tract and BG totals:

    • ACS 2015-2019
      • At Census Tract level, the sum of population is 328.016242 and the sum of Hispanic or Latino is 61.755289
         (in millions)
      • At Block Group level, the sums are exactly the same as for tracts
    • Census 2020 
      • At Census Tract level, the sum of population is 334.735155 and the sum of Hispanic or Latino is 65.329087
      • At Block Group level, the sums are exactly the same as for tracts
Reply
  • over 2 years ago

    I just got data for the entire US and Puerto Rico from NHGIS for the counts and levels you identified. My totals are different from the ones you derived, and I find no inconsistencies between the tract and BG totals:

    • ACS 2015-2019
      • At Census Tract level, the sum of population is 328.016242 and the sum of Hispanic or Latino is 61.755289
         (in millions)
      • At Block Group level, the sums are exactly the same as for tracts
    • Census 2020 
      • At Census Tract level, the sum of population is 334.735155 and the sum of Hispanic or Latino is 65.329087
      • At Block Group level, the sums are exactly the same as for tracts
Children
  • over 2 years ago in reply to Jonathan Schroeder

    Thanks, Jonathan!

    I should have been clearer in my post about the geographic selection. When I select all the states (including Hawaii, Puerto Rico and Alaska), my numbers match up -- just like yours.

    However, I was extracting only for contiguous United States -- excluding the three -- and still find the totals inconsistent. for example, my census tract totals are 329.82 and 62.57 million for total and hispanic population, respectively while my census block group totals are 324.41 and 59.15. This is for ACS 2016-2020. It may or may not be an error on NHGIS level that the geographic selection only applies to the block group level table and not to the census tract one. Was just curious it is was an artifact of new disclosure avoidance methods or not.

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