Short-term storage is a stable predictor of fluid intelligence whereas working memory capacity and executive function are not: A comprehensive study with Iranian schoolchildren

The present study investigates the simultaneous relationship among short-term memory (STM), working memory capacity (WMC), executive function (EF) and fluid intelligence (Gf) across two age groups using multi-group confirmatory factor analysis (MG-CFA). A total of 356 children recruited from primary school in Tehran were tested. Gf was assessed by the four subtests of the Cattell Culture Fair Intelligence Test. Digit Span, Letter Span, and the Kim Karad Visual Memory Test were used for measuring STM. WMC was measured by Backward Digit Span, Backward Letter Span, and Counting Span. Finally, the Stroop Task, the Wisconsin Card Sorting Test, and the Keep Track task measured EF. The key results derived from the analysis of the considered four-way relationships showed that STM did predict individual differences in Gf for both age groups with the same regression value. Furthermore, the contribution of specific WMC and EF variance (with their STM component removed) changed across age demonstrating a substantial instability for these constructs.