A Review of Acceptance and Commitment Therapy (ACT) Empirical Evidence: Correlational, Experimental Psychopathology, Component and Outcome Studies

Central thesis and objectives

This article analyzes the general empirical evidence concerning Acceptance and Commitment Therapy (ACT) with the aim of providing a comprehensive and updated overview of the empirical status of this therapeutic model. The author argues that in the years prior to publication, the debate about ACT had narrowed to very specific issues (especially the methodological comparison with CBT in randomized controlled trials), losing sight of the overall picture of the ACT model and its evidence. The objective is to summarize the current evidence from different types of empirical studies relevant to ACT—correlational, experimental psychopathology and component, and outcome studies—to assess the extent to which they support or contradict the model's postulates.

Theoretical framework

ACT is a model of psychological intervention philosophically rooted in Functional Contextualism and theoretically rooted in Relational Frame Theory (RFT). Functional contextualism is a pragmatic variety of contextualism that understands events as ongoing actions in context, with the goals of prediction and influence with precision, scope, and depth. ACT emphasizes workability as a truth criterion, so thoughts are not evaluated as correct or incorrect but as useful or not for living according to personal values. RFT proposes that human beings learn to relate stimuli under arbitrary contextual control, and this relational repertoire (relational frames) has three properties: mutual entailment, combinatorial entailment, and transformation of functions. RFT has important implications for psychopathology and psychotherapy: once a person has a minimal relational repertoire, the transformation of aversive functions cannot be prevented; attempts to change or suppress the content of relational networks are not psychologically sound (verbal relations work by addition, not subtraction); and it is possible to directly change the context of relational responding without changing its content.

The central concept of ACT is Experiential Avoidance Disorder or destructive experiential avoidance: a transdiagnostic functional category proposing that most psychological disorders share a common functional pattern of deliberate attempts to avoid or escape from aversive private events. ACT seeks to dismantle this inflexible repertoire by generating psychological flexibility through two fundamental therapeutic principles: (1) promoting values clarification and values-consistent actions, and (2) promoting involvement in valued ends when feared private events are present. Clinical methods include creative hopelessness, values clarification, cognitive defusion, self as context, and the use of paradoxes, metaphors, and experiential exercises.

Argument development

Previous reviews of ACT evidence. The author contextualizes the controversies between Hayes et al.'s (2006) first comprehensive review, Öst's (2008) critical review, and replies by Gaudiano (2009) and Levin and Hayes (2009). Conclusions are: (1) ACT is superior to control conditions and treatment as usual; (2) more evidence is needed to determine whether it is better than established treatments; and (3) ACT RCTs can be methodologically improved, although this is characteristic of any emerging psychotherapeutic approach.

Correlational studies. The relationship between experiential avoidance (measured primarily with the AAQ) and psychological symptoms/constructs is reviewed. Twenty studies (total N = 3323) obtained correlations between AAQ and depression measures (weighted r = .55), and 14 studies (total N = 3043) between AAQ and anxiety (weighted r = .52). Over 30 longitudinal and mediational studies showed that experiential avoidance mediates the relationship between various risk factors and psychological symptoms across areas including chronic pain, work settings, stressful life events, and other psychological constructs.

Experimental psychopathology and component studies. Three types are reviewed: (1) studies on the effect of experiential avoidance repertoire in experimental tasks, showing that participants with high AAQ scores have lower tolerance, greater discomfort, and worse performance; (2) studies on the effect of acceptance versus suppression instructions, generally favoring acceptance; and (3) studies on brief ACT protocols versus control-based protocols, representing the most coherent strategy, with results consistently showing that acceptance-based protocols are more efficacious than control-based ones.

Outcome studies. Studies are reviewed in detail across: clinical psychology (depression, anxiety disorders, OCD, social phobia, GAD, math anxiety, subclinical worries, trichotillomania, psychotic symptoms, borderline personality disorder, addictive behaviors, at-risk adolescents); health psychology (chronic pain, smoking cessation, cancer, epilepsy, weight loss, diabetes, tinnitus, postsurgical recovery, multiple sclerosis, HIV, lupus); and other areas (sport performance enhancement, chess, work stress, resistance to validated treatments, prejudice and stigma reduction). Four summary tables are presented. In general, effect sizes are large and tend to improve at follow-up. ACT has shown efficacy with extremely brief interventions in many studies.

Processes of change. It is highlighted that ACT researchers have placed great emphasis on studying change processes. Data suggest ACT works through its main hypothesized processes: reduction of experiential avoidance and cognitive fusion. This is consistent with the experimental psychopathology and component literature.

Implications

The author concludes that ACT's fundamental postulates have strong empirical support from correlational, experimental, and outcome evidence. ACT is noted as a therapy with singular characteristics: it is explicitly rooted in specific philosophical assumptions (functional contextualism) and in a contextual theory of human language and cognition (RFT). Its psychopathology model based on experiential avoidance or psychological inflexibility and its clinical methods are precisely directed at dismantling it. The comparison of ACT versus CBT is acknowledged to be in its beginnings, and better controlled studies with larger samples are needed. The importance of future RFT research for improving ACT clinical methods is emphasized, specifying the transformations of functions involved in cognitive defusion and values clarification exercises, and the verbal processes involved in the use of therapeutic metaphors.

Significance and contribution

This article constitutes one of the most comprehensive reviews of ACT empirical evidence published at the time, distinguished by its systematic organization of evidence into four categories (correlational, experimental psychopathology, component, and outcome) and by covering virtually all available ACT literature through winter 2009. Unlike previous reviews that focused mainly on RCTs, this article provides an integrated view of how different types of evidence converge to support the ACT model. The summary tables of outcome studies in clinical psychology, health psychology, and other areas offer an exhaustive reference tool. The article also clearly identifies limitations of existing evidence and points to RFT research as the most promising avenue for ACT's future advancement, a perspective that differentiates ACT from other contextual or third-wave therapies.

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Checklist de verificación / Verification checklist

• PDF leído completo antes de redactar / Full PDF read before writing
• Datos numéricos verificados contra el artículo original / Numerical data verified against original article
• Correlaciones ponderadas correctamente reportadas / Weighted correlations correctly reported
• No se atribuyen datos a estudios incorrectos / No data attributed to wrong studies
• Ambas versiones (ES/EN) contienen la misma información factual / Both versions contain the same factual information