Guilty Until Proven Innocent: Field Drug Tests and Wrongful Convictions

This year 773,000 people will be arrested based on field drug tests with known accuracy problems.

This report provides the first-ever comprehensive analysis of presumptive drug field test usage across law enforcement agencies in the United States. Inexpensive and fast, these tests have become a tool of choice for law enforcement agencies. Unfortunately, they are notoriously imprecise and are known to produce “false positives,” leading to frequent wrongful arrests and wrongful convictions.

Utilizing a nationwide survey of agencies, the report offers national estimates on the frequency of test usage, finding that each year approximately 773,000 drug-related arrests involve the use of presumptive tests. Although the true error rate of these tests remains unknown, estimates based on the imperfect data that are available suggest that around 30,000 arrests each year involve people who do not possess illegal substances but who are nonetheless falsely implicated by color-based presumptive tests. On a per capita basis, Black Americans experience these erroneous drug arrests at a rate 3x higher than White Americans.

While factors like eyewitness misidentification, false confessions, or prosecutorial misconduct have been previously cited as leading causes of wrongful convictions, these new results indicate 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 in the United States.

​Download the report here.

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