PISA Maths-Reading index and its relationship with gender and levels of performance.

• PISA 2018 Mathematics minus Reading scores are related to individual differences. • Gender is globally linked to positive Maths-Reading values. • Individual level or performance affects to Maths-Reading correlations. • Combined effects of gender and performance affect to Maths-Reading correlations. The Spanish PISA 2018 students sample (>35,900 fifteen-year-old students) has been analysed by calculating the Mathematics minus Reading scores of all individuals in the sample, relating this Maths-Reading index to the personal and educational characteristics of the respondents. Results of the first step of the analysis show that the positive Maths-Reading Index values (higher scores in maths than in reading) are mainly related to gender, and negative values (higher scores in reading) are mainly related to the joy of reading and to a series of factors linked to interest and respect for other cultures, among others. Subsequently, the individual level of global performance is taken into account with a cluster analysis generating groups of high, medium and low performers. Changes in factors affecting the Maths-Reading index when this level-based grouping is considered are analysed, showing the importance of grade repetition for low performers and the influence of socio-economic factors for medium performers, while high performers are affected especially by non-cognitive aspects such as self-concept or expected occupational status. Finally, combined effects of gender and level of performance are taken into account, showing that the factors affect male and female students differently for the disparate performance-based groups. This study contributes to a more precise knowledge of the main factors associated with students' tendency to have better scores in mathematical items than in reading items or vice versa, and to distinguish the differential role of personal and environmental factors not only globally, but also when gender and performance levels are taken into account. Studying this personal tendency is significant as it is related to students' study choice, especially Science-Technology-Engineering-Mathematics (STEM) degrees. [ABSTRACT FROM AUTHOR]