DRE Agreement With Any Drug Administration Differed From Correct Drug-Class Identification

In a laboratory DEC study, agreement with administration of any active drug was a different endpoint from correctly identifying the drug class. The reported percentages should not be merged into one cannabis-impairment accuracy claim.

The study compared several drug conditions

Heishman, Singleton and Crouch studied 48 volunteers in a double-blind laboratory experiment involving alprazolam, d-amphetamine, codeine and marijuana. The study examined drug-evaluation observations and officers’ opinions against controlled administration and toxicology.

Across the studied drug conditions, 76% of opinions about impairment were consistent with administration of an active drug. Drug-class opinions were consistent with toxicology under the stated classification standards in 32% of cases. Those figures had different targets.

A broader target is easier to satisfy

An opinion can agree that some active drug was administered while naming the wrong category. That outcome counts differently when the question is any drug versus the particular class. The denominator and scoring rule are therefore essential to any percentage.

These were pooled results across multiple drugs. Neither 76% nor 32% should be quoted as marijuana-specific sensitivity or as the probability that a cannabis-positive driver was functionally impaired.

Controlled administration was not a driving reference

Knowing which drug was given is valuable experimental information, but it is not the same reference as independently measured driving performance. The timing of examinations relative to drug effects also matters; the report identified marijuana as an exception to its near-maximum plasma scheduling.

For a useful interpretation, state the target explicitly: administration, toxicological detection, drug category or performance. The study’s main lesson here is how much an apparent accuracy figure can change when the endpoint changes, even within one experiment.

Related: How the reference specimen changes a cannabis accuracy claim.

Research cited

Heishman SJ; Singleton EG; Crouch DJ; Journal of Analytical Toxicology; 1998. Laboratory Validation Study of Drug Evaluation and Classification Program: Alprazolam, d-Amphetamine, Codeine, and Marijuana.