That which you worship, you do not understand.
International Association of Chiefs of Police
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The Drug Influence Evaluation is a medical test made up by traffic policemen. DIE tests are administered by police who call themselves Drug Recognition Experts.

A DRE officer stops a driver, and suspects drugs. The DRE examines the driver, looking for supposed physical "indicators" of the presence of various drugs. The officer concludes that the driver is impaired by a drug, orders forced blood testing, and—before the results come back— predicts the presence of a drug belonging to a particular drug category.

Then, when the blood test does come back showing that drug, the officer's amazing prediction is taken as proof that the driver must have been impaired by that drug. How else could the officer have made that amazing prediction? [Here's how.]

Some drivers refuse blood testing. When these people are prosecuted, DRE officers' opinions are used, without toxicology testing, as evidence of drug impaired driving.

How traffic-police think DIEs work

Drugs cause physical effects. Traffic police have convinced themselves they can puzzle cause and effect backward, from physical effects to impairing drug(s).

Traffic police believe they have proof DIEs work. First, in day to day use the DIE appears to validate itself. Drug Recognition Experts predict specific drugs, and later laboratory testing finds exactly those drugs!  Amazing.

Second, police cite "scientific studies" that claim to prove DIEs are accurate. Later you'll learn what peer-reviewed science says about the validity of those studies.

Does any of this seem odd to you?

  • A highly accurate scientific test was made up by two policemen (wonderful people, but not scientists), who did no scientific evaluation to see whether their homemade test actually worked.
  • When the federal agency that promotes these tests finally got around to field testing the tests, the "validation study" they issued turns out to have been written by an agency employee [LAPD 173]. The employee who works for the agency that promotes the tests reported that the tests the agency promotes are... 94% accurate! NHTSA published its employee's report in-house, without allowing independent outside experts to check for gross scientific errors and exaggerations.
  • Key elements of the traffic-police DIE are unstandardized, which means no one can tell you —or DRE trainees!— how the test is done. But the test is still highly accurate. The traffic-police DIE is highly accurate no matter how it's done!
  • Medical boards and state governments certify medical doctors to diagnose drug impairment after 7 to 10 years of medical training. Traffic police certify other traffic police to diagnose medical drug impairment after days of police training.
  • Is this story possible? No, it isn't. The traffic-police Drug Influence Evaluation story can't be true. Here at DECP.US I'm gonna splain to you why and how it isn't true.

    Good people, bad science

    Nothing here at DECP.US suggests police are liars or NHTSA's DIE validation contractors are cheats. Police are honest and honorable. We're talking about guys who run toward the sound of gunfire; they are better men than me. The lady police are better men than me. But they are not scientists.

    The fine folks at NHTSA and the IACP are good people doing their best. But mostly they are not scientists.

    Science is harder than it looks. Validating diagnostic tests is harder than it looks. Validation methods based on common sense lead immediately to immense over estimations of test accuracy in a way that is entirely invisible to non-specialists. NHTSA's in-house traffic-police DIE validation science looks like real science. But it's not. DIEs are crackpot science, not because someone is cheating, but because they were invented and tested by wonderful people who lacked the specialized training necessary to know the subtle tricks required to validate a diagnostic test in a scientifically meaningful way.

    DECP.US is not about these good people, it's about that bad science.