It is a popular notion that personality traits may influence the state of a person's physical health. The image of the stressed, aggressive businessman being liable to have a heart attack is so common as to have become a cliché, yet, as we shall see, it has little evidential basis. If personality traits do influence health, then this is one of the prime reasons to measure personality traits in medical settings. However, there are difficulties in establishing the true nature of the relationship between personality and health, including measurement, the distinction between subjectively reported symptoms and objective signs of illness, and the direction of causation. In addition, it is virtually impossible to assess the amount of risk that personality traits pose on their own – the separate impact they might have over and above that of poverty or working conditions, for example. The best solution is to try to design studies and use statistical analyses that are appropriate to the study of complex interactions. In this chapter we first discuss models of personality and health, then go on to describe more specific areas such as personality, stress and heart disease. Finally, we briefly discuss the connection between personality and clinically defined ‘psychosomatic’ disorders such as irritable bowel syndrome and globus pharyngis.
Achievements of trait research
Traits are alive and well. We contend that the research reviewed demonstrates that stable individual differences in personality are quantifiable and related to a variety of important criteria. Four key areas highlight the advances of contemporary trait research: psychometrics, biological bases, integration with mainstream psychology, and real-world applications. For each area, we will consider briefly both the accomplishments of trait research, and how future research might address remaining problems.
The current bullishness of trait psychologists begins with the slaying of the dragon of situationism, by exposure of the fallacies of Mischel's (1968) critique of traits (Eysenck and Eysenck, 1980), and increasingly sophisticated data on cross-situational behavioural consistency, cross-cultural generality and temporal stability (see chapters 2 and 3). We now have personalities again, and it is exciting to see their return (Goldberg, 1993). Furthermore, psychometricians have reduced competing structural models of broad ‘superfactors’ to a manageable number. Both Eysenck (1997) and proponents of the Big Five (McCrae, 2009; Saucier and Goldberg, 1996) have developed models with strong claims to validity, with some overlap with respect to the E and N factors. Possibly, the two models can be reconciled as alternative descriptions at different levels of generality, within a hierarchical personality model. Additional traits may also become elevated to superfactor status as research findings accumulate (Hogan and Hogan, 2002).
Introduction: neuropsychological approaches to personality
In this chapter we discuss the hypothesis that personality is an expression of individual differences in brain function. There are several reasons for linking personality traits to neural systems. First, there is the evidence from behaviour genetics discussed in the previous chapter. If personality traits are partially caused by genetic factors, then there must necessarily be a biological influence on traits, encoded within the person's DNA. Of course, the influence of the genotype on brain structure and function is likely to be influenced by interaction with the environment. Second, there is striking evidence for radical personality change resulting from brain damage (see Powell, 1981, and Zuckerman, 1999, 2005, for reviews). Damage to the frontal lobes of the cerebral cortex is notorious for disruption of personality; the person may become unstable, impulsive and even aggressive (depending on the exact region damaged). Third, there is some, though not unequivocal, evidence that traits correlate with biological indicators of brain functioning, such as the responses gathered from functional magnetic resonance imaging and electroencephalographic studies. Correlations between brain and trait parameters suggest that we might develop psychobiological theories of personality traits. Such theories should describe how individual differences in the functioning of specific brain systems influence long-standing individual differences in behaviour.
However, there are various difficulties involved in building a psychobiological theory of personality traits. First, the complexity of the task is daunting.
Introduction: the nature of stress
Stress is a necessary part of life, but the impact it has on people varies, depending partly on their personality traits. In this chapter, we discuss how personality, stress reactions, styles of cognitive appraisal and coping relate to stress vulnerability and emotional problems arising from stress. The most straightforward research on personality and stress is correlational in nature. As we shall see, there is abundant evidence that shows traits, especially neuroticism (N), are associated with high levels of stress symptoms, including mental disorders. Beyond correlational studies, there are several more difficult issues. One issue is whether high N is truly a causative factor on stress outcomes: perhaps increased N is simply a concomitant of stress, with no direct causal influence. A second theme which we will develop is that ‘stress’ refers to a multitude of concepts that may be only loosely related, including exposure to disturbing events, physiological response to threat, biases in cognition and disruption of everyday social interaction. A third theme is that of person–situation interaction in the stress process, consistent with the interactionist approaches to personality reviewed in chapter 2.
It is useful to begin with some definitions of stress. Because the term ‘stress’ is imprecise, it is interpreted in many different ways. Therefore, below, we give a brief overview of the concept of ‘stress’ before we consider, in the rest of the chapter, how it relates to personality traits.
The first edition of this book was motivated by the authors' perception that research on personality traits had reached a ‘critical mass’ that would justify a textbook focusing on the trait as an organising construct for understanding personality. We are gratified by the success of the first edition, which satisfied the need for a book on personality based on modern scientific research. Since the publication of the first edition, other authors appear to be distancing themselves from the traditional Hall of Fame text that we criticised initially. It is a relief to see the Hall of Fame approach receding into the distance so that the teaching of personality can be based on empirical data rather than historical relics.
We appreciate the feedback that we received from colleagues concerning the first edition. These comments helped to shape both the content and organisation of this new edition. We encourage academic faculty, practitioners and students to continue to share their opinions of the text with us. So far as content is concerned, the challenge has been to keep pace with the surge of new data and theorising on traits. In consequence, all chapters have been updated, and readers will note that a high proportion of the studies cited are recent. To better keep up with new developments, we invited a new author to join the original duo: Dr Whiteman brings expertise in health, epidemiology and lifespan aspects of personality.
Dimensions of personality describe variations in behavioural dispositions in the population. Because most personality dimensions are normally distributed, it is easy to assume that ‘abnormality’ lies at the tails of the distributions. For example, people with very high neuroticism scores might suffer much from anxiety, and those with very high conscientiousness scores might be disablingly rigid. However, might there be qualitative, as opposed to statistical, differences between the bulk of the population and a few individuals with very unusual personalities? The concept of personality disorder or abnormal personality lies within the domain of psychiatry and clinical psychology. Strangely, although it alludes to human personality variation, until the 1990s personality disorder attracted relatively little interest from differential psychologists studying normal personality. Conversely, the largely medically oriented researchers in the field of personality disorders have until recently shown little interest in either normal personality dimensions or the techniques of differential psychology.
Instead of benefiting from progress in the taxonomy of normal personality traits, psychiatric nosologists turned to medicine and biology rather than psychology for models for classifying psychopathology. They continue to do so because the philosophical assumptions underlying current psychiatric nosology stipulate that psychiatry is a branch of medicine, that discrete categories of mental disorder exist, and that there is a clear distinction between normality and pathology.
It is commonplace for books on personality to make little or no mention of the research on personality disorders, let alone try to integrate normal and abnormal personality research, though there are exceptions (Larsen and Buss, 2006).
Thus far, we have outlined the general case for approaching the study of personality via the trait concept. Before developing this argument, we must look briefly at the relationship between trait theories and other approaches to personality, such as psychoanalysis and humanistic psychology. There are three main reasons for so doing. First, trait theory has not developed in isolation from alternative theories. Allport (1937), for example, explicitly stated that his trait theory was an attempt to unify the diverse personality theories of his day. It is important to identify both those features of trait theories which are distinctive from other approaches and areas of common ground between trait theories and the alternatives. An issue of particular importance is consistency of behaviour. As we shall see, the idea of temporal stability in behaviour and mental life is not exclusive to trait psychology. Second, our thesis in this book is that trait psychology is becoming the dominant paradigm for personality research. This chapter offers some reasons why the trait approach may be more successful than competing ones, such as its use of the scientific method, and its ability to accommodate empirical data on behavioural consistency and stability. Third, although psychoanalysis and humanistic psychology are minority interests among personality scientists, these disciplines continue to develop and to inform empirical research. New constructs inspired by these fields, such as implicit or unconscious personality traits, may extend the range of traits that should be accommodated within an evidence-based account of personality.
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