Hierarchical Joint Modeling of Item Responses and Response Times on an Intelligence Test Battery: Detecting Unusual Examinee Behavior and Heterogeneous Relationships Between Working Speed and Ability

Mental speed is a multidimensional construct that encompasses three distinct time-related measures: reaction time, processing speed, and tempo, the latter of which is defined as the rate at which individuals respond to items varying in difficulty. This study applies van der Linden’s (2007, 2009) hierarchical model to jointly analyze item responses and response times from 1,620 adults taking the nine core subtests of the Reasoning and Intelligence Online Test (RIOT; https://riotiq.com). Using Bayesian estimation of the van der Linden model, results showed strong model fit across subtests, with near-zero correlations between examinee ability and examinee tempo for verbal tasks (r = -.209 to .136) and stronger negative correlations for visuospatial tasks (r = -.467 to -.769), supporting predictions from dual process theory. Item intensity and sensitivity positively moderated response times with difficulty on most subtests, indicating that item characteristics were the cause of longer response times for more difficult items. Few examinees (2.5%) exhibited dual misfit in responses and times, but the Figure Weights subtest revealed anomalous slow responding. These findings demonstrate that tempo (i.e., examinee response times) are independent of cognitive ability level and that correlations between the two are spuriously caused by item characteristics. Implications for intelligence testing and future experimental validation are discussed.