To create a DNA profile, scientists analyze 15 different STRs (yellow boxes) scattered among our chromosomes. Sharing the same number of repeats at any particular STR is relatively common—typically 5% to 20% of people share the same pattern at any one STR site. But it is the combined pattern of STR repeats at multiple sites that is unique to a person; the more STRs tested, the more discriminating the test becomes.