Ninewells Hospital & Medical School, Dundee, DD1 9SY

An introduction to Inference-Based Therapy (IBT)


Behavioural treatment for Obsessive Compulsive Disorder (OCD) is traditionally based on an Exposure and Response Prevention (ERP) model; an approach which is evidence-based but often under-used. Since high levels of distress can be experienced during treatment it can be difficult for the patient to fully engage and, in some cases, for the therapist to deliver therapy. The recommended frequency (15-20 sessions), duration (90 minutes), and setting (community rather than office-based) make it challenging for services to deliver optimised treatment.

Inference Based Treatment (IBT) offers an alternative treatment option. In contrast to the cognitive appraisal model which informs ERP, IBT theorises that obsessions arise through a faulty reasoning system which leads to recurrent doubts and faulty inferences. Cognitive interventions in IBT focus on helping patients to identify the reasoning errors that lead to obsessions. IBA is traditionally delivered in a clinic setting, in time limited sessions, and does not generate the levels of anxiety that are a necessary component of ERP.

A comparison of CBT/ERP and IBT

The following table draws some comparisons between 'traditional' CBT/ ERCP and IBT.

Characteristic CBT/ERP IBT
Main theory Learning theory Reasoning theory
Nature of intrusions Extension of normal beliefs. Intrusions are seen as normal. Intrusions are not necessarily normal
Underlying error Appraisal (and meaning) is at fault Reasoning is faulty
Focus of treatment Appraisal of thoughts and extinction of feared response. Target is primarily the anxiety. Doubt and Inferential confusion.
Intervention In vivo exposure and response prevention (ERP) and cognitive interventions to challenge appraisal of thoughts. Cognitive interventions designed to resolve OCD-related doubts without performing compulsions, and ‘reality testing’ exercises.

IBT formulation

The image below shows how formulation works in IBT. It is based on the treatment of repugnant obsessions, which are those obsessions associated with fears of paedophilia and similar concerns. They are often difficult to treat because developing a hierarchy-based treatment programme can be difficult.

What’s the evidence base to support treatment?

ERP is undoubtedly more 'established' but IBT is developing an evidence base to support its use. We have compared the number of RCTs (randomised controlled trials) involving both treatments, and this is summarised in the table below.

Characteristic CBT/ ERP IBT
Total no. of RCTs 42 3
Total patients (N) 2,226 189
Type of control group (active vs inactive) 36:6 2:1
Baseline Y-BOCS score (Mean ± SD) 24.5 ± 4.5 22.3 ± 5.2

Advantages and disadvantages


  • The therapy can be delivered via videoconferencing - a significant advantage during a pandemic.
  • The evidence base, although not as large as ERP, suggests comparable effectiveness.
  • It doesn't rely on increasing anxiety via exposure in order for it to work. This can be helpful in particular cases:
    • Where someone has repugnant obsessions (e.g. paedophilic intrusions) and exposure-based treatment is challenging.
    • Where someone finds it hard to engage in exposure because of the anxiety.
    • If someone has already tried ERP but it has not resulted in significant improvement.


  • Not everyone has the IT equipment or confidence to engage in videoconference-based therapy.
  • Some people may have such severe symptoms that they need inpatient treatment.
  • If it is being delivered remotely, it is a little harder to engage in the family work that is important for all OCD treatment.

References and further reading

Descriptions of the model

O'CONNOR K, KOSZEGI N, AARDEMA F, VAN NIEKERK J, TAILLON A. An Inference-Based Approach to Treating Obsessive-Compulsive Disorders. Cognitive and Behavioral Practice. 2009; 16(4): 420-429.

AARDEMA F, O'CONNOR K. Dissolving the tenacity of obsessional doubt: Implications for treatment outcome. Journal of Behavior Therapy and Experimental Psychiatry. 2012; 43(2): 855-861.

JULIEN D, O’CONNOR K, AARDEMA F. The inference-based approach to obsessive-compulsive disorder: A comprehensive review of its etiological model, treatment efficacy, and model of change. Journal of Affective Disorders. 2016; 202: 187-196.

AARDEMA F, O`CONNOR KP, DELORME M-E, AUDET J-S. The Inference-Based Approach (IBA) to the Treatment of Obsessive–Compulsive Disorder: An Open Trial Across Symptom Subtypes and Treatment-Resistant Cases. Clinical Psychology & Psychotherapy. 2017; 24(2): 289-301.

Clinical trials

O'CONNOR KP, AARDEMA F, BOUTHILLIER D, FOURNIER S, GUAY S, ROBILLARD S, PÉLISSIER MC, LANDRY P, TODOROV C, TREMBLAY M, PITRE D. Evaluation of an Inference‐Based Approach to Treating Obsessive‐Compulsive Disorder. Cognitive Behaviour Therapy. 2005; 34(3): 148-163.

MORITZ S, DIETL C, KERSTEN JF, AARDEMA F, O'CONNOR K. Evaluation of Inference-Based Therapy (Doubt Therapy) as a Self-Help Tool for Obsessive-Compulsive Disorder. Journal of Cognitive Psychotherapy. 2015; 29(4): 315-330.

VISSER HA, VAN MEGEN H, VAN OPPEN P, EIKELENBOOM M, HOOGENDORN AW, KAARSEMAKER M, VAN BALKOM AJ. Inference-Based Approach versus Cognitive Behavioral Therapy in the Treatment of Obsessive-Compulsive Disorder with Poor Insight: A 24-Session Randomized Controlled Trial. Psychotherapy and Psychosomatics. 2015; 84(5): 284-293.


MATHER A, CHRISTMAS D, MATTHEWS K, O’CONNOR K. Repugnant Obsessions: Using an Inference Based Approach to Treat OCD [Poster]. Presented at Royal College of Psychiatrists International Congress 2018. Birmingham; 24-27 June 2018.

MATHER A, CHRISTMAS D, O’CONNOR K. The Inference-Based Approach: An alternative to Exposure and Response Prevention for OCD? Presented at 9th World Congress of Behavioural and Cognitive Therapies 2019. Berlin; 17-20 July 2019.

Last Updated on 8 November 2023 by David Christmas
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