General intelligence in middle school students from different Russian regions: Results of PISA-like tests

This study is aimed at investigating the contribution of the general intelligence factor if six PISA domains (reading, mathematical, scientific, financial literacies, global competence, and creative thinking) are combined in one measurement instrument. For achieving our goal, items based on the PISA frameworks are developed, students in grades 5–8 from three different Russian regions are assessed, and three IRT models (unidimensional, multidimensional, and bifactor) are applied to process the data. In addition, the correlations from the multidimensional model are estimated to examine the degree of cognitive specificity and mixture modeling is implemented to investigate ability differentiation across grades. Statistical analysis reveals that the bifactor model comprising one general and six specific factors, has a better fit in each grade. Based on this model, we compute the variance explained by the general factor, with the estimates varying between 60% and 70%. In general, the pure variance explained by specific factors does not exceed 10%. The correlations are above 0.40 in each grade and the averaged associations tend to increase from 6th to 8th grade, although they are smaller in years 6 and 7 compared to year 5. The general ability differentiation effect is observed in grades 6 to 8 and is not present in grade 5. Specific ability differentiation is more pronounced in reading literacy, especially in grade 5 to 7. The results obtained are discussed from the perspective of the ability and developmental differentiation/dedifferentiation problem.