In Reply.—Dr Amoroso et al suggest that
tobacco use, not available in our study, may have confounded the association
between benzodiazepine use and the risk of motor vehicle crash in the elderly.
Given the lack of an effect with short-acting benzodiazepines, and the fact
that tobacco use is unlikely to be differentially distributed according to
the type of benzodiazepine (long- vs short-acting), confounding by tobacco
use is unlikely to account for our results.
Drs Green and Wintfeld suggest that insufficient information was available
to control for confounding by health status. We used the chronic disease score
to obtain a measure of health status based on patterns of drugs dispensed
in the year prior to the index date.1Thus,
cardiovascular disorders, diabetes, and other chronic conditions and their
severity are taken into account. Moreover, exposure to other drugs with central
nervous system effects, including antidepressants, were controlled for separately
in the analysis. It is unlikely that, after controlling for these accurate
measures of health status, confounding would still be present.