Choice RT shares roughly a quarter of its variance with general IQ

Correct: B — Around r = -0.3 to -0.5 (faster RT, higher g), with choice RT correlating more strongly than simple RT

Deary, Der & Ford (2001) tested roughly 900 56-year-olds from a Scottish population cohort on simple RT, four-choice RT, and a battery of cognitive tests. Choice RT correlated about r = -0.5 with general intelligence (faster responders scored higher) and simple RT around r = -0.3, with no inflation by reliability artifacts. The result corroborated three decades of mental-chronometry findings that processing-speed measures share substantial variance with psychometric intelligence, while making clear that RT is a meaningful correlate but not a substitute for full IQ testing. Subsequent work has linked these RT–g relationships to white-matter integrity and aging trajectories.