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Posted on: June 2, 2015

MCAO Notified of Errors in FBI DNA Profile Frequency Data

PHOENIX - Late in the afternoon of May 28, 2015, the Maricopa County Attorney’s Office received notice of a recent FBI Bulletin describing an amendment to the 1999 and 2001 FBI Short Tandem Repeats (STR) Population Data due to clerical and transcription errors that occurred during the creation of the original database. This data provides the basis for calculating the frequency that a particular DNA profile would be found within a given population.

The FBI advises that these discrepancies are “unlikely to materially affect any assessment of evidentiary value.” The agency will announce its findings in the July 2015 issue of the Journal of Forensic Sciences and include data demonstrating the minimal effect of these statistical differences on DNA profile probabilities. Additionally, the American Society of Crime Lab Directors (ASCLD) recently advised all of its member laboratories that while some statistical frequencies increase in rarity and others decrease, “[d]ifferences between the statistics calculated using the original tables and the corrected tables are minimal.” Crime laboratories that have already begun to evaluate these differences, including the Phoenix Police Crime Lab, have reached the same conclusion.

In keeping with its ethical duties, the Maricopa County Attorney’s Office is diligently reviewing existing cases to ensure that adequate notifications are made to the courts and defense counsel in order for this information to be properly assessed from a legal and scientific standpoint.

The FBI is also in the process of making this data available on its public website,


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