The present investigation examined empirically the influence of neuroticism on the relation between locus of control and depression, first as a moderator with specified interaction effects, and secondly as a mediator in the path from locus of control to depression. Levenson's internality, powerful others and chance (IPC) locus of control scales, the Eysencks' EPQ-R neuroticism scale and a depression inventory were completed by 162 university students aged 17–57 years (mean=27.9, SD=10.3). There were no significant differences between sexes on any mean score. Controlling for sex and age, externality, neuroticism and depression were significantly correlated (p<0.001), but only chance locus of control and neuroticism predicted depression. In the absence of significant interaction and quadratic effects, multiple regression analyses did not support neuroticism as a moderator, but as a partial mediator in the relationship between chance locus of control and depression. Path analysis showed that the total effect size was very large. The influence of neuroticism was discussed in terms of the “depressive paradox” (self-blame and uncontrollability co-existing in depressed individuals), the multidimensional aspects of locus of control, and implications for treating depression.
Recently the personality traits of locus of control and neuroticism have been examined together for their impact on various clinical conditions (Beautrais, Joyce, & Mulder, 1999; Horner, 1996; Murray, Hay, & Armstrong, 1995; van den Heuvel, Smits, Deeg, & Beekman, 1996; Wise & Mann, 1993). Locus of control involves a general enduring belief in the controllability of outcomes of events in one's life (Rotter, 1966). According to Rotter, it ranges from a belief that such outcomes are controllable (internal locus of control orientation or internality), to a belief that outcomes are generally beyond personal control (external locus of control orientation or externality). Neuroticism is a personality trait that has provided a useful integrative psychobiological construct in depression research ( Murray et al., 1995). Eysenck (1967) proposed that it originates from the sensitivity of the limbic–autonomic nervous system that tends to be highly reactive to environmental and psychological stimuli. People with high neuroticism are easily startled and agitated.
For example, Horner (1996) used Rotter's (1966) locus of control scale and the neuroticism scale of the Eysenck personality questionnaire (EPQ; Eysenck & Eysenck, 1975) with 173 community dwelling adults to show that an interaction of stressful life experiences, very high externality and very high neuroticism could predict reported physical illness. Neither external locus of control or neuroticism independently had a significant, direct effect on illness. For psychological conditions, the two variables are also salient. Murray et al. (1995) found with an all-female sample that external locus of control of moods and neuroticism were related to seasonal affective disorder, but extraversion, psychoticism and the EPQ Lie scale were not. Similarly, Beautrais et al. (1999) demonstrated that externality and neuroticism could reliably distinguish between young suicide attempters and non-attempters, but extraversion could not. In a large sample of 3107 elderly participants in a Dutch longitudinal study, van den Heuvel et al. (1996) found that women tending toward externality and neuroticism reported more depressive symptoms when experiencing various impairments in cognitive functioning. For men experiencing memory impairment, only neuroticism affected levels of depression.
There are, however, some problems with the conceptual and empirical aspects of the associations between locus of control, neuroticism and depression. These problems include the “depressive paradox”, the multidimensional nature of locus of control, and the functions of moderators and mediators.
