Study Finds Field Drug Test False Positive Results Lead to Wrongful Arrests


Tens of thousands of people are wrongfully arrested for crimes based on a false positive result from a field drug test each year, according to a recent study by researchers at the University of Pennsylvania. The research, which analyzed data available from public agencies across the country, found that the use of presumptive field tests in drug arrests is likely the largest known factor contributing to wrongful arrests and convictions in the United States.

The research was conducted by the University of Pennsylvania Penn Carey Law School’s Quattrone Center for the Fair Administration of Justice, a national research and policy center created to foster structural improvements to the U.S. criminal legal system. The study analyzed survey data and national estimates of drug arrests to determine the impact of field drug tests on wrongful arrests, as well as their impact on subsequent prosecutions and criminal convictions.

The study found that approximately 773,000 of the more than 1.5 field drug tests conducted in the United States each year are performed with color-based presumptive tests despite known reliability issues, including false positive results that incorrectly indicate the presence of controlled substances. Although the exact error rate for the tests has not been determined, the data suggests that about 30,000 people who do not possess drugs are falsely implicated by the tests each year.

“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. Now, this landmark study by the Quattrone Center demonstrates the scope of the harm done by these inaccurate test kits, including the disproportionate impact to African Americans,” Des Walsh, founder of the Roadside Drug Test Innocence Alliance, said in a report from the Penn Carey School of Law. “Based on this study, we look forward to working with law enforcement and other interested parties to implement policies and adopt better testing techniques to substantially reduce the tragic number of innocent people arrested and convicted because of these false tests.”

Tests Designed For Preliminary Use Only

The report notes that the tests were originally adopted as only a preliminary test for the presence of controlled substances because of their unreliability and potential to return false positive results. However, the widespread use of the tests has negatively impacted the integrity of the legal system. Nearly 90% of prosecutors surveyed by the researchers said that guilty pleas are permitted in their jurisdictions without verification of a field test by an accredited toxicology lab. 

“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,” said 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.”

About two-thirds (67%) of the drug labs in a national sample reported that they were not asked to verify the results of positive tests in cases resolved by a plea agreement. Nearly a quarter (24%) said they do not receive samples for testing when the results of a field test are available. When samples are received, nearly half (46%) of the labs surveyed do not conduct tests to confirm the field test if a guilty plea has already been entered in the case.

The research also reveals racial disparities in the impact of false positive test results. The study found that a Black person is three times more likely than a white person to be arrested with a false positive from a field test.

The research also suggests that the manufacturers of field test kits for drugs are not being transparent with law enforcement officials about the reliability of the tests. When the Jacksonville Sheriff’s Office (JSO) in Florida recently discovered that field-testing kits for cocaine had produced false positives, the agency immediately discontinued the use of the kits. When the owner of the cocaine test kit company used by JSO was asked about the false positives, he responded that this was not the first time they had false positives and that this is the “nature of the beast,” according to a policy brief from the Quatrone Center.

In another interview, he stated, “I have no sense of the scale. I don’t know if it’s been one case or five. But I can’t imagine it’s horribly widespread.”

The report recommended several policy changes to reduce the reliance on presumptive field drug tests and subsequent wrongful arrests and convictions. Recommendations include regular blind audits of cases using field tests to determine the error rate. The report also recommends that police cite and release people arrested for drug possession until a lab test can verify the results of a field test. The report also calls for confirmatory testing whenever a guilty plea is accepted. The researchers also recommended that the use of field drug tests be reduced or eliminated or that more accurate tests be used.

“The relative volume of drug cases in criminal cases overall, combined with the widespread reliance on error-prone field testing in arrests, indicate that this is a significant and underexplored vector for wrongful convictions,” said Quattrone Center academic director and law professor Paul Heaton. “Law enforcement, prosecutors, defense attorneys, and the public all want an accurate criminal adjudication process. Reforming how presumptive tests are used could advance this shared goal.”



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