Human factors and ergonomics research could benefit from focusing more strongly on individual differences--especially trait variables. The present study suggests the analysis of moderator effects as a promising way to enhance understanding of trait variables and process control performance. Process control performance was studied by analysing moderator effects of general mental ability (GMA) and need for cognition (NC) on risky decision-making (RDM) and performance. Fifty engineering students were trained on a process control task using a computer-based simulation for three hours and tested twice thereafter. Risky decision-making was measured using a computerised gambling task while GMA and NC were assessed with questionnaires. Risky decision-making in interaction with each GMA and NC explained variance in performance over and above variance explained by the single effects. In conclusion, the analysis of moderator effects between individual difference variables and process control performance seems promising. Practitioner Summary: Individual difference variables affect learning and performance, but have often not been studied to any great extent in human factors research. This article suggests a promising approach to studying individual differences--moderator analyses--and illustrates how such differences can lead to a better understanding of what determines process control performance.