5

There are ACS 5 variables that are available at the tract level, but return null at the block group level. For example, median monthly housing costs:

http://api.census.gov/data/2014/acs5/?get=B25105_001E&for=tract:*&in=state:17%20county:001

http://api.census.gov/data/2014/acs5/?get=B25105_001E&for=block%20group:*&in=state:17%20county:001%20tract:00100

What does a null value signify? Is it that the variable is never available at the block group level, or just for some/most of the block groups?

5

Table B25105 is not available at the Block Group level. The appendices show which tables are available at the block group level.

  • That's a useful link, but doesn't quite answer my question. Is there any other reason, besides block group exclusion for a variable to be null? – fgregg Oct 23 '16 at 18:05
  • You are requesting an estimate at the block group level from Table B25105, but the Census Bureau does not publish that table at that geographic summary level. I guess they choose to return a null value in the API. – Kotebiya Oct 24 '16 at 2:04
  • I think that's right in this case, but I'm asking about null in general. – fgregg Oct 24 '16 at 2:21
3

A null result means that the variable has been suppressed for that geography. Some variables are always suppressed for a certain level of geometry, but even if a variable is usually available for a level of geometry, it may still be suppressed for a particular geometry because of:

  • Population Thresholds
  • Data Quality Filtering
  • Disclosure Review Board Rules

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