Alternate Name	Item#	Length	Source of Standard	Column #
Census Tract Block Group	362	1	Census	174-174

Description
This field is provided for coding the block group of patient's residence at time of diagnosis, as defined by the 2000 Census.

Rationale
A block group is a subdivision of a census tract designed to have an average of 1500 people, versus a census tract's average of 4500 people. All land area in the United States is described by a census block group in the 2000 Census. The Census Bureau publishes detailed population and socioeconomic data at this level. Block groups thus offer a high level of specificity for geographical and socioeconomic analyses.

A block group has no meaning in the absence of a census tract. Refer to Census Tr Certainty 2000 [365] to ascertain basis of assignment of Census Block Group 2000.

Codes

0	Census block group assignment was attempted, but the value could not be determined
1-9	Census block group values as defined by the Census Bureau
Blank	Census Block Group 2000 not coded

Note: The values 1 through 9 are nominal, with no hierarchy of values. This number determines the first digit of all the blocks which comprise the block group; for instance, census block group 3 would contain blocks numbered 3000 to 3999.

Comment
Numerous registries find the distinction between "attempted, could not be determined" (zero) and "not coded" (blank) to be useful for geocoding planning purposes.