Results of the verification protocol for the U74 and 430 arrays. Three analyses were done per array: allowing only perfect matches, allowing one mismatch per probe and allowing two mismatches per probe. Per analysis, probe sets are assigned to the highest quality group (the lowermost group in the figure). So if a probe set is 'entirely verified' in RefSeq, it is assigned to this group. If it is not 'entirely verified' in RefSeq but it is 'entirely verified' in UniGene Unique, it is assigned to this second group, and so on.