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Results

The four?tep regression analyses followed Baron and Kenny? (1986)
procedures to determine the presence of the mediated relationship. Due to the
inherent weaknesses of the stepwise regression, the conclusion might be
erroneous (Preacher, 2004). Therefore, the bootstrapping method was used to
test whether the mediated relationship was statistically significant. In this
analysis, if the indirect effect of Principal Leadership on Teacher Professional
Learning through Collaboration was significant, the mediating effect of
Collaboration was supported. This procedure produced a very similar (.156) and
statistically significant indirect effect. To conclude, the indirect effect of Principal
Leadership on Teacher Professional Learning through Collaboration is significant.

Table 3 also shows the ratios of the indirect effect in contrast with the total
effect and direct effect, and the statistical significance of the ratios. The indirect
effect of Principal Leadership on Teacher Professional Learning constituted a
significant 73.6% of its total effect on Teacher Professional Learning. In
other words, approximately 73.6% of the total effect of Principal Leadership
on Teacher Professional Learning is mediated by Trust. Further, the indirect
effect was 2.8 times of the direct effect of Principal Leadership on Teacher
Professional Learning. The R?quared mediation effect size and Preacher
and Kelley? (2011) Kappa?quared, both reported only for simple mediation
analysis, again indicated that the mediated effect is medium in size and
statistically significant.

Omnibus tests using the seven core areas of the Principal Leadership as
independent predictors also affirmed a small but significant mediating effect of
Trust on Teacher Professional Learning (Bootmean = .083, SE = .018). Results of
the omnibus tests for the direct effect (R簡 = .057, F(7, 961)= 15.166, p < .001.)
and total effect (R簡 = .126, F(7, 962) = 19.867, p < .001), also indicated small but
statistically significant direct effects and total effects of Principal Leadership
practices on Teacher Professional Learning.

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