Functional Driving Tests Need Validation for the Claim They Make, Even When Concentration Tests Are Limited
A 2019 perspective reviewed limitations of concentration-based and functional approaches to cannabis-impaired driving. Weakness in one approach does not automatically validate the other for every intended inference.
The methods address different observations
A concentration test measures a chemical in its specimen, while a functional task measures performance under test conditions. Neither observation alone establishes every element of exposure, impairment, cause and driving risk.
Functional deficits can have multiple explanations
The review discussed difficulty distinguishing cannabis-related effects from other influences, including age and medication use. A task that detects reduced function still needs evidence for any claim that cannabis specifically caused it. Detecting a problem and attributing its cause are different validation questions.
The perspective was historically bounded
The source's assessment described the literature available at the time. It should not be presented as proof that no later method could be validated or as a current statement of local driving law. A particular device or protocol requires its own supporting evidence.
Interpreting the evidence
The review supports asking what a test was validated to detect and against which reference. It does not establish that every poor performance proves cannabis impairment or that a limited concentration relationship means functional evidence can be accepted without scrutiny.
Related reading: interpreting cannabis tolerance claims.
Research reference
Ginsburg BC (2019). Strengths and limitations of two cannabis-impaired driving detection methods: a review of the literature. The American journal of drug and alcohol abuse. doi:10.1080/00952990.2019.1655568.
This analysis draws on the supplied review abstract.
