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Report Finds Inaccurate Field Drug Tests Major Cause of Wrongful Convictions

by Matthew T. Clarke


A report published in January 2024 by the Quattrone Center for the Fair Administration of Justice at the University of Pennsylvania’s Carey School of Law revealed that false positives in presumptive field test used in drug arrests are one of the most common, and possibly the most common, cause of wrongful arrests and convictions. The report, entitled “Guilty Until Proven Innocent: Field Drug Tests and Wrongful Convictions,” utilized a nationwide survey of law enforcement agencies and forensic drug labs to make its determinations.

Using data from the survey and national estimates of drug arrests, the report estimates the impact of (1) false positives in field drug tests on wrongful arrests, (2) racial inequity in arrests, (3) the subsequent prosecutions, and (4) criminal convictions. It reported that approximately 773,000 of the over 1.5 million annual U.S. drug arrests involve the use of color-based presumptive field tests. Although the exact error rate for the tests is unknown because they require a subjective determination by the arresting officer, available data suggest around 30,000 people are arrested in the U.S. each year due to false positives of the field tests.

“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,” according to Quattrone Center Assistant Director Ross Miller, the lead author of the report. “But in our criminal legal system, where pleas bargaining is the norm and actual fact-finding by trial is exceedingly rare, these error-prone tests have become the 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 tests were designed to be used as a preliminary screening tool because of their unreliability. Yet, nearly 90% of prosecutors responding to the survey reported that guilty pleas are accepted in their jurisdictions without verification of the field test by an accredited laboratory. Sixty-seven percent of labs reported not being required to review samples in cases resolved by plea agreements. Twenty-four percent of the labs did not even receive samples when field test results were available. Forty-six percent reported that no confirmatory test would be performed if a guilty plea had already been entered.

“Every year, tens of thousands of innocent Americans are arrested on the basis of $2.00 roadside drug test kits that are known to give false positives,” said Des Walsh, Founder of the Roadside Drug Test Innocence Alliance. “Now, this landmark study by the Quattrone Center demonstrates the scope of the harm done by these inaccurate test kits….”

The report recommends reducing reliance on field drug tests, regular blind audits to establish the field test error rate for specific officers, issuing a citation only until the results of the field drug test are confirmed by a certified drug lab, and requiring lab confirmation even when a guilty plea is entered alongside a right to withdraw the plea should the lab results show the sample is not a controlled substance. Ultimately, the report recommends limiting or banning the use of the current, inaccurate field drug tests.


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