A review of obsessive intrusive thoughts in the general population
Highlights
► This literature review assesses the validity of the continuum between intrusive thoughts and obsessions. ► Previous research examining intrusive thoughts in nonclinical samples is considered. ► Additional conditions for the continuum between intrusive thoughts and obsessions are proposed.
Introduction
Intrusive thoughts are central in the current understanding of Obsessive–Compulsive Disorder (OCD), as outlined in DSM IV criteria (American Psychiatric Association [APA], 1994) and in current cognitive models. Pioneering research by Rachman and de Silva (1978) illustrated that intrusive thoughts, similar in content and form to clinical obsessions, are a common experience for nonclinical individuals (80% of a nonclinical sample). Comparisons with a clinical sample highlighted differences in frequency, duration and intensity of intrusive thoughts; clinical participants also appraised their thoughts as less acceptable, less able to resist and less dismissible. Correspondingly, Clark and Rhyno (2005) described a severity continuum between obsessions and intrusive thoughts, with frequency, distress and perceived thought control being among the distinguishing factors.
The continuum hypothesis forms the premise for current cognitive models of OCD, which converge on the proposition that an individual's understanding of ‘normal’ intrusive thoughts is central in the development and maintenance of OCD. Cognitive theories differentially emphasise the role of beliefs that fuse the intrusive thought to the event or action (Rachman, 1997, Rachman, 1998), that one is responsible for harm coming to oneself or others (Salkovskis, 1985, Salkovskis, 1999), and meta-cognitive beliefs about the significance of intrusive thoughts (Wells and Matthews, 1994, Wells, 1997). Such beliefs determine the individual's appraisal of intrusive thoughts, which in turn determines subsequent cognitive and behavioural responses. Previous research consistently supports the role of interpretations of intrusive thoughts in the maintenance of OCD; this research is built on the supposed accuracy of the continuum hypothesis.
Rassin and Muris (2006) challenged the continuum hypothesis as an overinterpretation of the finding from Rachman and de Silva (1978) that psychology experts were unable to accurately classify ‘abnormal’ obsessions. In a reanalysis of the data from the original study, Rassin and Muris supported this finding; however, in a subsequent replication of the classification task, the authors reported greater accuracy by experts (psychotherapists) and by psychology undergraduates. The accurate distinction between clinical and nonclinical intrusive thoughts indicates recognisable differences in thought content. However, as Rassin and Muris highlighted, both groups still did not perform at perfect level. Therefore, some obsessions may be similar to intrusive thoughts, whereas others are more ‘bizarre’.
In a further challenge to the continuum hypothesis, Julien, O'Connor, and Aardema (2007) critique previous findings on the universality of intrusive thoughts for inconsistencies in definition and methodology, and generalisations from student populations. The authors concluded that there is insufficient support for the appraisal model of OCD. Julien et al. provide a considered critique of the methodology of research on intrusive thoughts; however, the paper lacks a detailed consideration and comparison of the findings. The current paper aims to fill this gap; through an up-to-date narrative review of research investigating obsessive intrusive thoughts in nonclinical populations, the accuracy of the continuum hypothesis is assessed. Additional research since 2007 is considered alongside previous work. The assumption that intrusive thoughts are a common nonclinical experience is first assessed through discussion of research findings on their prevalence in nonclinical samples. The similarity between intrusive thoughts and obsessions is next considered in a discussion of research on the nature of intrusive thoughts in nonclinical samples, including, themes, triggers, appraisals, and responses. The paper concludes with a proposed revision to the continuum hypothesis based on highlighted differences between ‘normal’ intrusive thoughts and clinical obsessions.
For the purposes of this review ‘intrusive thoughts’ are defined as cognitions that are spontaneous, disruptive, difficult to control and unwanted (Rachman, 1981) and may include verbal thoughts, images, or impulses. A review of the literature was conducted on 11/01/2012 via web of science and PsycINFO databases; search words such as intrusive thoughts, nonclinical obsessions, and intrusions were used. The search was limited to journal articles written in English, published from 1978 onwards (published after Rachman & de Silva, 1978). A manual search of the references of each paper concluded the literature search. Empirical papers that assessed obsessive intrusive thoughts within a nonclinical sample (community, student, unspecified nonclinical) were included.
Section snippets
Prevalence of nonclinical intrusive thoughts
Questionnaire studies have asked nonclinical participants to endorse obsessive intrusive thoughts that they have ever experienced from a prescribed list, which has produced prevalence rates of 74% (Langlois, Freeston, & Ladouceur, 2000a), 88% (Salkovskis & Harrison, 1984) and 99% (Belloch et al., 2004, Purdon and Clark, 1993). The Obsessive Intrusions Inventory (OII/ROII) produced the highest endorsement figure; however, 16 items were excluded during the development of the OII because less than
Conclusions
Intrusive thoughts are hypothesised to be similar to clinical obsessions, with the defining difference being degree not kind (Clark & Rhyno, 2005); however, the literature reviewed here does not fully support this hypothesis. Clinical obsessions are experienced in greater frequencies (re-experienced) to their nonclinical counter-parts, which supports a continuum of quantitative difference. However, additional differences in content, appraisals and response were highlighted. Clinical obsessions
Limitations and future directions
Addressing the limitations of the reviewed research, such as methodological biases and inconsistent definitions, will further our understanding of intrusive thoughts. The body of research may be biased toward the assumption that intrusive thoughts do occur in nonclinical populations: questionnaires assessing appraisals, etc., which assume the presence of intrusive thoughts, could be leading for participants; other studies have only included participants who report frequent or distressing
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