Variances in Census Block data for two files

Hello and Happy Holidays!

I am using the new 2015 5-Year Data set to update numbers using the Income, Minority and Language ACS Files. When I ran the income numbers for Essex County Massachusetts Census Blocks, I used two data sources: "household income in the past 12 months (B19001)" and "Median Household Income in the last 12 months (B19013). Unfortunately B19013 is missing some Census Blocks (26 to be specific). 6 of those Census Blocks are missing from our specific region. Has anyone run across this in their work? We have a small region, so I have to run the numbers by Census Blocks to get at the specific info we're looking for.



  • Hi Angie,
    These missing block groups may be related to the Census Bureau's new rules for suppressing median income and earnings estimates in cases where the margin of error is larger than the estimate. "Beginning in data year 2015, a new methodology was applied to the 5-year dollar-based medians and quintile limits that suppresses the table for the geographic area if the margin of error is larger than the estimate itself. "

    Table B19013 is one of the tables affected by their new methods:
  • Thanks Mark! It's curious that there would be such a high margin of error. Do you have any insight into that?
  • MOEs are almost entirely driven by the number of cases - interviews - in the group. Census blocks, depending on how many housing units they have, may have 1 or NO interviews in a 5 year period. Where there are few cases, MOEs are sky-high. The ACS really is simply not reliable at the census block level for anything; the only point of releasing block data is to make possible custom geographic aggregations. Even block groups, or in some cases tracts, have very high MOEs.
  • Thanks Patty, just to clarify--while decennial census data are available down to the block level, block groups are the smallest geography for which ACS data are released.
  • Thanks to Angie for pointing out the missing data.  

    And thanks to Mark for suggesting that it might be due to a change in suppressing rules for median incomes in 2015 - I was not aware of this change and it is important information!

    I was curious to see if I could replicate Angie's results and, if so, what the median income and MOEs were in 2014 for the missing block groups.

    I found similar results - table B19013 for Essex County MA has 13 fewer block groups (534 versus 547) than B19001 for the same year or than B19013 for 2014.  Angie reported 26 missing block groups but I think this may come from AFF row count comparisons that have two rows for each block group.

    Of the 13 missing block groups, 5 had MOEs larger than the estimate in the 2014 version of table B19013.  

        2010-2014 2010-2014
    Missing block groups:   Median Income MOE
    250092011002   40556 46651
    250092052002   36719 79314
    250092063003   40781 46185
    250092102001   79464 56366
    250092173001   39397 41674
    250092181002   65982 26585
    250092221001   93750 33670
    250092502004   47115 39097
    250092508005   34590 19621
    250092511002   27917 36972
    250092609002   78194 67735
    250092610001   50667 29415
    250092682001   70726 37365

    So Mark's hypothesis that it might be due to the new suppression rule seems plausible.  Additional evidence: the 2014 table had 16 block groups where the MOE was larger than the estimate and the 2015 table does not have any.

    However, if the values were suppressed because of large MOEs, why isn't there any annotation?  The rows are just missing - no annotation is present for these block groups.  Census really should include annotation if these data values are being suppressed. 

  • Hi David,

    We are aware of the issue with the missing annotation and we are hoping to have a solution for next year's release.

    KaNin Reese
    Census Bureau