Long-term stability of standard deviation of lateral position in neurocognitively normal and impaired individuals

The standard deviation of lateral position (SDLP), or degree to which individuals adjust lane position while driving, is frequently used in human factors studies, including the evaluation of the acute effects of medication and illicit drugs. In addition, there is increasing interest in such “real world” outcomes in the tracking of neurologic disorders and their treatment. However, there are limited data regarding SDLP testretest reliability over protracted periods. Previous research has demonstrated that cognitive impairments associated with HIV infection may result in decreased driving performance. In order to examine the appropriateness of using SDLP as a long-term outcome for patient groups, we assessed the stability of SDLP performance on a PC-based driving simulator in HIV seropositive subjects tested at 1) a 3 month retest interval [a time frame common to clinical trials; Short Interval Group], and 2) a year or longer retest interval [a time period over which one might track changes in neurologic patients; Long Interval Group]. The Short Interval Group consisted of 16 HIV seronegative and 13 early stage HIV-positive subjects. Overall test-retest reliability (rs) was .71 (p < .001). The Long Interval Group (n = 30) was comprised of cognitively stable HIV-positive individuals (39% with cognitive impairment). Reliability for this cohort was .72 (p < .001). SDLP is a reliable measure for periods ranging from months to years when assessed in cognitively stable subjects. This metric may thus serve as a useful tool in tracking long-term changes in driving abilities.