Background: Neuroticism measures are very popular in psychopathological research, but it is unclear how useful neuroticism is in studies of the aetiology of psychopathology.
Method: A conceptual examination was made of the literature on the association of neuroticism and psychopathology, the ontological status of neuroticism, the purport of neuroticism questionnaires, and causal issues.
Results: The research on which neuroticism is built has historically been based solely on the factor analyses of the common adjectives used to describe usual behaviours. An abundance of studies have shown that neuroticism scores predict life stress, psychological distress, emotional disorders, psychotic symptoms, substance abuse, physical tension-related symptoms, medically unexplained physical symptoms, and health care utilisation. This evidence suggests that neuroticism scales index vulnerability to many forms of negative affect and psychiatric disorder. However, the associations do not clarify the nature of this vulnerability nor the underlying psychobiological mechanisms. We present evidence that neuroticism scores reflect a person's characteristic (or mean) level of distress over a protracted period of time. In this perspective, even prospective associations of neuroticism with mental health outcomes are basically futile, and largely tautological since scores on any characteristic with substantial within-subject stability will predict, by definition, that characteristic and related variables at later points in time.
Conclusion: Neuroticism is not an explanatory concept in the aetiology of psychopathology, since it measures a person's characteristic level of distress over a protracted period of time. This situation will not change until knowledge becomes available about: (i) the mechanisms that produce high neuroticism scores (and, therefore, also psychopathology) and (ii) its neurobiological substrate. Only then will we understand why neuroticism appears to "predict" the outcomes it predicts.