From Florida’s voter file as of 2005:
Percentage of blacks among registered voters: 12%
Percentage of blacks among those whose voter file entry is missing the apartment number: 19%
Percentage of blacks among those whose voter file entry is missing or has an incorrect zip code: 25%
That is from an analysis by Michael McDonald. He concludes:
bq. It is my opinion based on an examination of easily identifiable address errors on the Florida voter registration file that such errors more frequently occur among African-American Florida registered voters than registered voters of other races. These errors will cause disproportionate problems with the delivery of mail ballots to African-Americans, as proposed by the Florida Democratic Party as a means to conduct a second 2008 presidential primary within the state.
While a second FL primary appears unlikely — or so I glean from this — such problems with voter files may affect other aspects of elections, including the ability of parties and others who purchase these files to target voters and the extent of mismatches between the voter file and voters’ own identification materials (where required).