Assessing intraindividual variability in sustained attention: Reliability, relation to speed and accuracy and practice effects

We investigated the psychometric properties of competing measures of sustained attention. 179 subjects were assessed twice within seven day's time with a test designed to measure sustained atten-tion, or concentration, respectively. In addition to traditional performance indices [i.e., speed (MRT) and accuracy (E%)], we evaluated two intraindividual response time (RT) variability measures: standard deviation (SDRT) and coefficient of variation (CVRT). For the overall test, both indices were reliable. SDRT showed good to acceptable retest reliability for all subtests. For CVRT, retest reliability coeffi-cients ranged from very good to not satisfactory. While the reversed-word recognition test proved highly reliable, the mental calculation test and the arrows test were not sufficiently reliable. CVRT was only slightly correlated but SDRT was highly correlated with MRT. In contrast to substantial practice gains for MRT, SDRT and E%, only CVRT proved to be stable. In conclusion, CVRT appears to be a poten-tial index for assessing performance variability: it is reliable for the overall test, only moderately corre-lated with speed, and virtually not affected by practice. However, before applying CVRT in practical assessment settings, additional research is required to elucidate the impact of task-specific factors on the reliability of this performance measure. Key words: concentration; sustained attention; intraindividual variability; coefficient of variation; reliability; response tim