EVIDENCE LIBRARY
Norwegian Driver Study’s Nonsignificant Single-Drug Finding Did Not Establish Benzodiazepine Driving Safety
A case–control study compared injured drivers with drivers in normal traffic. Small subgroups and different specimen types limit broad claims from its negative single-drug result.
A case–control study compared injured drivers with drivers in normal traffic. Small subgroups and different specimen types limit broad claims from its negative single-drug result.
The comparison
Researchers tested injured drivers’ blood and roadside drivers’ oral fluid, applying equivalent concentration cutoffs for comparison. Psychoactive substances were detected more often among injured drivers than in normal traffic.
The largest risk estimates involved alcohol with other substances and multiple-drug exposure. Benzodiazepines were detected in 0.8% of the normal-traffic group. Single non-alcohol substance categories were not significantly associated with injury in the reported analysis.
Precision and measurement
A nonsignificant estimate can reflect limited numbers rather than absence of effect. Several combination estimates had very wide confidence intervals. Matching cutoffs across blood and oral fluid also does not make the specimens biologically identical.
The investigators identified the small case group and unknown nonresponse as important limitations. The study outcome was being an injured driver, not a direct psychomotor test.
Forensic interpretation
Do not use this study to declare that a positive benzodiazepine finding is harmless or proves crash causation. Examine the particular compound, concentration, matrix, timing, other substances, and driving evidence. Population associations and an individual driver’s functional state answer related but different questions.
Source paper
Original analysis of the supplied journal article, identified as PMC3489595.