Evaluating organizational stress-management interventions using ...

32 RANDALL, GRIFFITHS, COX
Table 1). This would lead naturally to the conclusion that the intervention
was ineffective in improving well-being.
Preanalysis checks confirmed the suitability of the data for repeated
measures ANCOVA analysis (see Table 2): The usual significance level of
p 5 .05 could be applied to the testing of effects. The results of the repeated
measures analysis of covariance are presented in Table 2. After controlling
for variance in the dependent variable accounted for by age, F(1, 33) = 6.13,
p 5 .05, the test of within-subjects effects revealed one significant interaction:
Exposure to the Intervention 6 Time, F(1, 32) = 6.83, p = .01; etasquared
.17. None of the other within-subject effects (the main effect of time
and the other interaction effects), were significant, F 4 3.24, p 4 .08. This
interaction (with adjusted means) is shown in Figure 1. None of the other
between-subjects effects were significant.
Table 3 shows the changes in exhaustion scores for the exposed and not
exposed groups separately. Exploration of the interaction term indicated
that from similar preintervention worn-out scores, F(1, 36) = 1.27, p 4 .05,
the scores of the two groups diverged to result in a significant difference in
postintervention exhaustion scores, F(1, 36) = 10.3, p 5 .01. This divergence
Figure 1.
Interaction effect (Study 1: Railway staff).