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Inconsistent findings on mental health difficulties and risk of involvement in terrorism
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There has been an increasing focus on the potential role of mental health difficulties in the process of violent radicalisation into terrorism. In part, this has been fuelled by studies appearing to show high prevalence rates in some samples of terrorists. However, findings are inconsistent, with some studies reporting higher rates than those observed in the general population, some lower, and others that are comparable to those observed in the general population.
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What is this review about?
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This review synthesises the prevalence rates of mental health difficulties in terrorist samples (Objective 1 – Prevalence) and prevalence of mental health disorders pre-dating involvement in terrorism (Objective 2 – Temporality). The review also synthesises the extent to which mental health difficulties are associated with terrorist involvement compared to non-terrorist samples (Objective 3 – Risk Factor).
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In addressing these objectives, the review offers an initial assessment of what we refer to as the mental health-terrorism hypothesis (that mental health difficulties are a risk factor for terrorist involvement). Tentative support for the hypothesis would be provided where studies, when collated, suggest higher rates of difficulties in terrorist samples than those expected in the community.
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The review distinguishes between mental disorders, suspected mental disorders and psychological problems. These are collectively termed mental health difficulties.
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What is the aim of this review?
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This Campbell Collaboration systematic review focuses on mental health and its association with terrorist involvement. The review examines evidence based on 56 papers reporting on 73 terrorist samples.
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What studies were included?
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For Objective 1, studies that report rates of mental health difficulties in terrorist samples are included. Studies were eligible even if the period after the terrorists became involved in terrorism is included. We identified 56 papers reporting on 73 terrorist samples that met this criterion.
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For Objective 2, studies from Objective 1 were included where they specifically reported rates of difficulties and where those difficulties emerged before the terrorist became involved in terrorism (or was first detected as being involved). Ten studies were included in this component of the review.
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Finally, for Objective 3, we included studies that compared rates of mental health difficulties in terrorist samples with non-terrorist samples. Nine eligible studies were included here.
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What are the main findings of this review?
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Our findings do not support the assertion that there are remarkably high rates of mental health difficulties in the terrorist population. As a benchmark, we estimate that the lifetime prevalence rate of diagnosed mental disorder in the general population is 29%. For Objective 1 (Prevalence) we report that the lifetime prevalence rate of diagnosed mental disorder in terrorist samples was 17.4%. This increased to 23.2% for the studies reporting lifetime prevalence rates of suspected disorder, and 28.5% for studies reporting any psychological problems.
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At any one time, 14.4% of those involved in terrorism may have a disorder or suspected disorder (as opposed to a psychological problem). When we isolated studies that reported rates prior to either engagement in terrorism or detection for terrorist offences (Objective 2, Temporality), the lifetime prevalence rate for any psychological problem was 27.8%.
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Finally, based on single study estimates, the odds of having a lifetime history of mental health difficulties between those involved in terrorist behaviour and non-terrorist offending varied depending on the comparison group (Objective 3, Risk Factor).
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What do the findings of the review mean?
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The findings do not offer support for the mental health-terrorism hypothesis. Trends in the data, however, may point to higher rates among some terrorist samples than others, and in particular among lone-actor terrorists.
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The synthesis could reflect methodological limitations in the studies included. Many studies rely on the media and court reporting, with researchers wholly reliant on these sources to determine whether or not mental health difficulties are present. This could lead to under-reporting (where such difficulties are not viewed as relevant to a criminal case for example) and thus deflate estimates reported in papers.
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That said, even among those papers that have not relied on open-source information, the evidence does not conclusively demonstrate that terrorist samples are characterised by higher rates of mental disorders or psychological problems than those expected in the community.
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How up-to-date is this review?
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The review authors searched for sources in April and May 2022, covering research up to December 2021.
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