Decision speed in intelligence tasks: is it really an ability?

We still understand surprisingly little about what gets called correct decision speed, or CDS, even though it has a place in the theory of fluid and crystallized intelligence. CDS refers to how quickly a person arrives at a right answer, measured through the latency of their correct responses. This study, with 186 participants, set out to test whether the construct behaves as a single broad factor or splits apart depending on the kind of problem being solved.

The main question we pursued was whether separate CDS factors emerge for different ability domains. In other words, when you time how long it takes someone to answer correctly on a fluid intelligence task (Gf) versus a crystallized intelligence task (Gc), do those two sets of response times reflect one general speed-of-deciding trait, or two? We also wanted to see how the correct response latencies lined up against Gf, Gc, and a more conventional measure of processing speed (Gs).

The data pointed to two factors rather than one. A CDS factor tied to Gf tasks and a CDS factor tied to Gc tasks could be distinguished from each other, though the two were correlated. Each one tracked its matching ability factor, and the Gc version of CDS showed only a weak connection to processing speed.

The picture got more complicated once item difficulty entered the analysis. Difficulty turned out to moderate how CDS related to the abilities, so a flat correlation between speed and ability can be misleading. We handled this by scoring item difficulty relative to groups of participants who differed in ability level, then comparing response speeds across those groups.

Doing it that way, clear speed differences showed up between the ability groups, and the shape of those differences held steady across easy and hard items alike. We make the case that comparing speed within difficulty bands defined by ability group is the more defensible approach for studying how ability level and decision speed hang together. Against that backdrop, the question of whether CDS deserves to stand as a broad ability in its own right remains open.