The test isn't perfect; that is, it has a margin of error of nine years in either direction. But in cases where police are trying to build a profile of an unknown person, the test can narrow the possibilities down to a generational cohort spanning about two decades. Previous attempts to do so have proved inaccurate, but this attempt at deriving a phenotypic human trait from DNA information is at least as accurate, if not more so, than other profiling methods like a similar means of determining eye color from DNA.