‘False positive’ field drug tests lead to wrongful convictions

A new Quattrone Center report shows that the use of presumptive field tests in drug arrests is one of the largest known contributing factors to wrongful arrests and convictions.

A new research report providing the first-ever comprehensive analysis of presumptive drug field test usage across law enforcement agencies in the United States has been released by the Quattrone Center for the Fair Administration of Justice at the University of Pennsylvania Carey Law School. Utilizing a nationwide survey of agencies, the report, “Guilty Until Proven Innocent: Field Drug Tests and Wrongful Convictions,” shows that the use of presumptive field tests in drug arrests is one of the largest, if not the largest, known contributing factor to wrongful arrests and convictions.

A police car with its lights on the roof.
Image: iStock/MattGush

The report uses survey data and annual national estimates of drug arrests to examine the impact of the tests on wrongful arrests and racial disparities, and their subsequent impact on prosecutions and criminal convictions. According to the report, approximately 773,000 of the more than 1.5 million drug arrests conducted in the United States each year involve the use of color-based presumptive tests, despite the known accuracy issues associated with the tests (e.g., false positives indicating the presence of an illegal drug where none exists). While the true error rate of these tests remains unknown, the available data suggests that around 30,000 people who do not possess controlled substances are falsely implicated by these tests and arrested each year.

“Presumptive field drug test kits are known to produce ‘false positive’ errors and were never designed or intended to provide conclusive evidence of the presence of drugs,” says Ross Miller, Quattrone Center assistant director and lead author of the report. “But in our criminal legal system, where plea bargaining is the norm and actual fact-finding by trial is exceedingly rare, these error-prone tests have become de facto determinants of guilt in a substantial share of criminal cases in the United States and, as a result, a significant cause of wrongful convictions.”

The report also details racially disparate impacts resulting from these tests, finding that a Black individual is three times more likely to experience a drug arrest with a false positive from a field test compared to a white individual.

Read more at Penn Carey Law.