WASHINGTON (dpa-AFX) - A new study has found that self-reported drug use is not an accurate measure in monitoring drug usage by drivers, underscoring the importance of conducting blood or saliva tests.
The new study by the Insurance Institute for Highway Safety or IIHS found that many people who drive vehicles within 24 hours of taking drugs are reluctant to admit it even if the drugs are legal. However, drivers who later tested positive for drugs reported taking them in their responses to questionnaires.
'These findings suggest that self-reported drug use is not a good measure for monitoring trends in drug use in this population,' says IIHS Senior Research Scientist Angela Eichelberger, the lead author of the paper.
Eichelberger noted that researchers lack access to good data on the prevalence of drug-involved driving nationwide.
Many drivers involved in fatal crashes are never tested for drugs. Even if they were tested, it is difficult to accurately estimate trends due to inconsistencies in testing procedures in various states and the different time periods.
The IIHS' analysis is based on two national roadside surveys in 2007 and 2013-14 of more than 7,000 drivers from 300 locations across the continental U.S.
For the two surveys, researchers gathered both biological and self-reported information from drivers. Specifically, researchers looked at the results related to cannabis, opioids, cocaine, antidepressants and benzodiazepines, which include drugs like Valium and Xanax.
According to the analysis, there is a possibility that some drivers who tested positive for drug use were telling the truth about not having used drugs in the past 24 hours, as chemical indicators of marijuana and other drugs can remain in the blood for a longer period.
In addition, not all of the drivers who reported taking drugs in the 24 hours prior to their participation in the survey tested positive.
According to the IIHS, these discrepancies could indicate that drivers might have been mistaken about when they took the drug or about the kind of medication they had taken.
The safety group noted that as a result, both biological tests and self-reporting are useful to understand the extent of the drug-impaired driving problem.
While biological tests provide important information, driver feedback can provide details about drug use that cannot be measured by tests, such as the frequency of use and mode of administration.
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