They point out that people of the same ethnic group share more DNA and would be more likely to match DNA than people outside these groups. DNA proponents respond that the FBI now keeps separate DNA databases for whites, Hispanics, Asians, and blacks. But critics contend these groupings are too large. In 1992, a National Academy of Sciences report agreed and recommended a temporary ceiling on odds for DNA matches. In 1996, however, a follow-up report found that the databases, combined with new formulas, gave accurate and powerful odds and lifted the ceiling.
Critics also complain of contamination.
Proponents agree that contamination can be a problem if people collecting and storing DNA evidence do not follow proper procedures. Finally, critics cite poor lab procedures. In one study in 1987-88, of 50 samples sent to the three major private DNA labs, two labs made mistakes on one sample. The overwhelming majority of court cases have allowed the introduction of DNA evidence. Some state legislatures have specifically written laws permitting it.