Post Hoc Analyses

2007). Further analyses were undertaken to explore possible reasons for this discrepancy.

As seen in Table 14 when initially entered Verbal Intelligence was a significant predictor of Spelling Performance; however when Language Ability was entered in the following step of the regression analyses the beta value of Verbal Intelligence decreased and became nonsignificant. In contrast, Tables 13 and 15 show that Verbal Intelligence remained a significant predictor of Reading and Math Performance when Language Ability was entered into the regression analyses but the beta value and significance level of Verbal Intelligence in relation to Reading and Math Performance was reduced.

83 Language Ability was therefore explored as a possible mediator based upon the reduction of Verbal Intelligence beta levels (Baron & Kenny, 1986) when Language Ability was entered in the regression analyses for research Models 1, 2 and 3.

According to Baron and Kenny (1986) the following four key criteria need to be met to confirm a mediation effect:

1) The independent variable must be significantly associated with the dependent variable;

2) The independent variable must be significantly associated with the suspected mediating variable;

3) The mediating variable must be significantly associated with the dependent variable while the independent variable is accounted for;

4) When entered into the model the mediator will reduce the association between the independent and dependent variable.

According to Baron and Kenny (1986) for a fully mediated pathway to be present the association between Verbal Intelligence and the academic performance areas should become non-significant when Language Ability is accounted for in the regression analyses. For a partially mediated pathway to be present the association between Verbal Intelligence and the academic performance areas will be reduced but remain significant. Figure 5 depicts the relationship between the mediating, independent and dependent variables.

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Figure 5. Diagram representing a mediation pathway (Baron & Kenny, 1986, p.1176)

Post Hoc analyses were conducted in order to investigate whether Language Ability mediates the effect of Verbal Intelligence on the dependent variables Reading, Spelling and Math Performance. A series of regression analyses using Reading, Spelling and Math as dependent variables were conducted based upon Baron and Kenny’s criteria.

The first series of regression analyses tested whether there was a significant association between the independent variable Verbal Intelligence and the individual dependent variables: Reading, F (1, 151) = 98.90, p <.001; Spelling, F (1, 151) = 37.32, p

<.01; and Math, F (1, 151) = 44.96, p <.01. Criteria 1 were met as the associations were all found to be significant.

A regression analysis was then conducted and confirmed a significant association between Verbal Intelligence and Language Ability, F (1, 151) = 128.38, p <.01 indicating that Criteria 2 was met.

Regression analyses were then conducted to explore whether Language Ability was significantly associated with the dependent academic variables after accounting for Verbal Intelligence. Criteria 3 was met as a significant association was found for Reading, F (2, 150) = 57.47, p <.01; Spelling, F (2, 150) = 30.44, p <.01; and Math, F (2, 150) = 25.20, p <.01.

Mediating Variable a b Independent Dependent Variable Variable c

85 In order for Criteria 4 to be met the association between the independent variable Verbal Intelligence and dependent variables Reading, Spelling and Math Performance needs to become either non-significant (indicating full mediation) or reduce in significance (indicating partial mediation) when the mediator variable Language Ability is entered in the regression analyses.

When Language Ability was entered into the respective regression analyses the effect of Verbal Intelligence remained significant for Reading Performance, F (2, 150) = 57.47, p < .01, and Math Performance, F (2, 150) = 25.20, p < .01. A closer examination of the

standardised beta coefficients indicated that when Language Ability was entered the beta value for Verbal Intelligence was reduced for both Reading (β = .63 reduced to β = .45) and Math Performance (β = .48 reduced to β = .34), indicating partial mediation.

In contrast for Spelling Performance when Language Ability was entered into the regression analysis the effect of Verbal Intelligence became non-significant F (2, 150) = 30.44, p > .05 indicating a fully mediated pathway.

Sobel tests were conducted in order to substantiate the mediation pathways identified by the regression analyses. A calculation tool provided by Preacher & Leonardelli (2006) was used to run individual Sobel tests for Reading, Spelling and Math Performance. Results indicated that Language Ability mediated the effect of Verbal Intelligence on academic scores in relation to Reading Performance (z = 3.05, p < .01), Spelling Performance (z = 4.06,

p < .01), and Math Performance (z = 2.06, p = < .05).

The effects of the mediator variable Language Ability on Reading, Spelling and Math Performance with associated standardised beta coefficients and significance levels are shown in Figures 6, 7 and 8 respectively.

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Figure 6. Language Ability as a Partial Mediator of the Association between Verbal Intelligence and Reading Performance. * p<0.05; ** p<0.01.

Note. The standardised beta weight for the direct pathway between the independent variable and the outcome variable is shown in parenthesis.

Figure 7. Language Ability as a Mediator of the Association between Verbal Intelligence and Spelling Performance. * p<0.05; ** p<0.01.

Note. The standardised beta weight for the direct pathway between the independent variable and the outcome variable is shown in parenthesis.

Language .68** Ability .58** Verbal Reading Intelligence Performance .45** (.63**) Language .68** Ability .52** Verbal Spelling Intelligence Performance .17 (.43**)

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Figure 8. Language Ability as a Partial Mediator of the Association between Verbal Intelligence and Math Performance. * p<0.05; ** p<0.01.

Note. The standardised beta weight for the direct pathway between the independent variable and the outcome variable is shown in parenthesis.