4.4 Partial correlations between executive function and academic achievements
After controlling for the influences of age, sex and the R’SPM scores, we could see purer correlations between academic achievements and EFs. All academic achievements had negative relationships with diagnosis status.
The mathematical achievement scores had positive correlations with the forward digit span scores (r = 0.16, P < 0.01) and the backward digit span scores (r = 0.23, P < 0.01) and had negative relationships with conversion times (r=-0.08, P < 0.05). The reading comprehension achievement scores had positive relationships with the total spatial span scores (r = 0.14, P < 0.05), the forward digit span scores (r = 0.21, P < 0.01), and the backward digit span scores (r = 0.16, P < 0.01) and had negative relationships with conversion times (r=-0.13, P < 0.05), the colour interference times (r=-0.13, P < 0.05) and the semantic interference times (r=-0.19, P < 0.01). The subtraction scores had a positive relationship with the backward digit span scores (r = 0.25, P < 0.01) and had negative relationships with conversion times (r=-0.16, P < 0.01), the colour interference times (r=-0.16, P < 0.05) and the semantic interference times (r=-0.20, P < 0.01). The semantic word scores had positive relationships with the forward digit span scores (r = 0.18, P < 0.01) and the backward digit span scores (r = 0.21, P < 0.01). It had negative relationships with conversion times (r=-0.29, P < 0.01), colour interference times (r=-0.29, P < 0.05) and semantic interference times (r=-0.19, P < 0.01) (see Table 4).
Table 4
Partial correlations between executive functions and academic achievements
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
1 ADHD diagnosis status (ADHD = 1, TD = 0) | - | | | | | | | | | | | |
2 Spatial span test-total scores | -0.40** | - | | | | | | | | | | |
3 Forward digit span | -0.08 | 0.11 | - | | | | | | | | | |
4 Backward digit span | -0.20** | 0.09 | 0.16** | - | | | | | | | | |
5 Digital span test-total scores | -0.20** | 0.14* | 0.74** | 0.78** | - | | | | | | | |
6 Conversion time (s) | 0.14* | -0.17** | -0.09 | -0.09 | -0.11 | - | | | | | | |
7 Colour interference time (s) | 0.17** | -0.10 | -0.05 | -0.09 | -0.11 | 0.16** | - | | | | | |
8 Semantic interference time (s) | 0.31** | -0.14* | -0.06 | -0.07 | -0.08 | 0.12* | 0.12 | - | | | | |
9 Mathematical achievement | -0.26** | 0.07 | 0.16** | 0.23** | 0.26** | -0.03 | -0.13 | -0.08* | - | | | |
10 Reading comprehension achievement | -0.35** | 0.14* | 0.21** | 0.16** | 0.25** | -0.09 | -0.13* | -0.19** | 0.51** | - | | |
11 Subtraction | -0.32** | 0.09 | 0.11 | 0.25** | 0.23** | -0.16* | -0.16* | -0.20** | 0.43** | 0.39** | - | |
12 Word semantic | -0.35** | 0.10 | 0.18** | 0.21** | 0.26** | -0.16* | -0.29** | -0.19** | 0.39** | 0.50** | 0.46** | - |
Note. Age, sex and the scores of R’SPM were controlled for. The spatial span test-forward and spatial span test-backward were unrelated to all kinds of academic achievements. *P < 0.05. **P < 0.01 |
4.5 Mediation analysis
Based on the partial correlation results, we considered ADHD diagnosis status (ADHD = 1, TD = 0) as the independent variable (X), the EFs that significantly related to four kinds of achievements as mediators (M), and the academic achievements as the dependent variates (Y) to establish SEMs and to analyse the independent contribution of each mediator on different academic achievements. All analyses were conducted after controlling for age, sex and R’SPM scores.
In the mediation pathway between ADHD status and mathematical achievements, forward and backward digit spans (Path 1–1) and semantic interference (Path 1–2) were mediators. In path 1–1, the total effect of an ADHD diagnosis on mathematical achievement was d=-0.19 (P = 0.01). The ADHD diagnosis status exerted significant direct effects on backward digit span (d=-0.29, P = 0.02) and mathematical achievements (d=-0.14, P < 0.01) but not on forward digit span. The two mediators together explained 26% of the total effect (dindirect effect=-0.05, P = 0.03). However, only backward digit span significantly moderated the effect of diagnostic status on mathematical achievements (d=-0.04, P < 0.05), which was partial mediation, and the effect ratio was 21% (see Fig. 1). However, in Path 1–2, the semantic interference did not have any mediating effects (see Fig. 2).
In the pathway between ADHD status and reading comprehension achievements, forward and backward digit span (Path 2 − 1), colour and semantic interference (Path 2–2), and total spatial span (Path 2–3) were mediators. In the three paths above, none of the mediators played mediating roles in reading comprehension achievements (see Fig. 3-Fig. 5).
In the pathway with subtraction, backward digit span (Path 3 − 1), colour and semantic interference (Path 3 − 2), and conversion (Path 3–3) were mediators. In Path 3 − 1, the total effect of diagnostic status was d=-0.31 (P = 0.02), and ADHD status had a significant direct effect on backward digit span (d=-0.29, P = 0.02). Backward digit span significantly moderated the effect of diagnostic status on subtraction (d=-0.06, P = 0.01), and the effect ratio was 19% (see Fig. 6). In Path 3 − 2, the total effect of an ADHD diagnosis on mathematical achievement was d=-0.29 (P = 0.01). ADHD diagnosis status exerted significant direct effects on colour interference (d = 0.32, P = 0.01) and subtraction (d=-0.24, P < 0.01) but not on the semantic interference. The two mediators together explained 17% of the total effect (d indirect effect=-0.05, P = 0.02). However, only colour interference significantly moderated the effect of diagnostic status on mathematical achievement (d=-0.03, P < 0.05), which was partial mediation, and the effect ratio was 10% (see Fig. 7). In Path 3–3, conversion did not have any mediating effects (see Fig. 8).
In the pathway with word semantics, forward and backward digit span (Path 4 − 1), colour and semantic interference (Path 4 − 2), and conversion (Path 4 − 3) were mediators. In Path 4 − 1, the total effect of an ADHD diagnosis on word semantics was d=-0.34 (P = 0.02). ADHD diagnosis status exerted significant direct effects on backward digit span only (d=-0.29, P = 0.02). The two mediators together explained 15% of the total effect (d indirect effect=-0.05, P = 0.01). However, only backward digit span significantly moderated the effect of diagnostic status on word semantics (d=-0.06, P < 0.05), which was partial mediation, and the effect ratio was 12% (see Fig. 9). In Path 4 − 2, the total effect of an ADHD diagnosis on mathematical achievement was d=-0.32 (P = 0.01). ADHD diagnosis status exerted significant direct effects on colour interference times (d = 0.21, P = 0.01) but not on semantic interference times. The two mediators together explained 19% of the total effect (d indirect effect=-0.06, P = 0.01). However, only colour interference significantly moderated the effect of diagnostic status on mathematical achievement (d=-0.04, P < 0.05), which was partial mediation, and the effect ratio was 12% (see Fig. 10). In Path 4 − 3, the conversion had a significant mediating effect (d indirect effect=-0.02, P = 0.01), and the effect ratio was 6% (see Fig. 11).