Alternate Name	Item#	Length	Source of Standard	Column #
	368	1	Census	165-165

Description
This field is provided for coding the block group of patient's residence at time of diagnosis, as defined by the 1970, 1980, or 1990 Census.

Rationale
A block group is a subdivision of a census tract or block numbering area (BNA). Not all of the United States was described by a census block group or BNA prior to the 2000 Census, but for areas assigned to block groups or BNAs, the Census Bureau published detailed population and socioeconomic data. Block groups thus offer a high level of specificity for geographical and socioeconomic analyses, where available.

A block group has no meaning in the absence of a census tract. Refer to Census Tr Cert 1970/80/90 [364] to ascertain the basis of assignment of CensusBlockGroup 70/80/90. Refer to Census Cod Sys 1970/80/90 [120] to ascertain the decade of reference.

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	CensusBlockGroup 70/80/90 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.