Stephen Kellett

SKcropI am a Consultant Clinical Psychologist in the NHS (RDASH NHS Foundation Trust) working in an in-patient setting and I am also an Honorary Senior Lecturer at the University of Sheffield.  I have worked in the NHS for many years in therapy services, training, supervision and senior management.

After completing my core CAT training in Manchester I have since qualified as a CAT psychotherapist. I am a trainer for the Catalyse/CAT North CAT Practitioner Training course and teach on CAT training courses around the country.  

I strive to increase the evidence base for CAT.  Current research includes conducting:

  • a large patient preference randomised controlled trial of psychoeducational CAT for anxiety in Pennine Care NHS Foundation Trust
  • a pilot and feasibility study of integrating repertory grids into the reformulation and ending process in the Manchester Specialist Psychotherapy Service.  
  • a meta analysis of idiographic change during CAT

Clinically, my real interest centres on helping people with long-standing interpersonal problems with the CAT model and approach and helping systems to work better around the service user using a CAT consultancy approach.



Gaskell, C., Kellett, S., Simmonds-Buckley, M., Curran, J., Hetherington, J., & Delgadillo, J. (2023). Long-term psychotherapy in tertiary care: A practice-based benchmarking study. British Journal of Clinical Psychology, 00, 1– 18.

Power, N., Kellett, S., & Gaskell, C. (2023). Effectiveness of cognitive analytic therapy for mixed anxiety and depression in the context of borderline traits: A quasi-experimental single case design evaluation. Journal of Psychotherapy Integration, 33(1), 34–46.


Easton K , Kellett S , Cooper M , Millings A , Varela J , Parry G (2021),
Blending Cognitive Analytic Therapy With a Digital Support Tool: Mixed Methods Study Involving a User-Centered Design of a Prototype App. JMIR Ment Health 2021;8(2): e20213 doi: 10.2196/20213

Stephen Kellett & Daniel Stockton (2021) Treatment of obsessive morbid jealousy with cognitive analytic therapy: a mixed-methods quasi-experimental case study, British Journal of Guidance & Counselling, DOI: 10.1080/03069885.2021.1929834

Merzhvynska, M. Simmonds-Buckley, M., Delgadillo, J., & Kellett, S. (2021). Trajectories of change in the therapeutic alliance during Cognitive Analytic Therapy for depression. Psychology and Psychotherapy Theory Research and Practice.

Wakefield, S., Delgadillo, J., Kellett, S., White, S. & Hepple, J. (2021) The effectiveness of brief cognitive analytic therapy for anxiety and depression: A quasi‐experimental case-control study. British Journal of Clinical Psychology. Early View (Open Access)


Kellett, S., Gausden, J. and Gaskell, C. (2020), The effectiveness of cognitive analytic therapy for borderline personality disorder: Utilizing a withdrawal experimental design to improve sensitivity to abandonment. Psychol Psychother Theory Res Pract.

Hallam, Craig & Simmonds-Buckley, Mel & Kellett, Stephen & Greenhill, Beth & Jones, Andrew. (2020). The acceptability, effectiveness, and durability of cognitive analytic therapy: Systematic review and meta‐analysis. Psychology and Psychotherapy: Theory, Research and Practice. 10.1111/papt.12286.

Kellett, S., Bee, C., Aadahl, V., Headley, E., & Delgadillo, J. (2020). A pragmatic patient preference trial of cognitive behavioural versus cognitive analytic guided self-help for anxiety disorders. Behavioural and Cognitive Psychotherapy, 1-8. doi:10.1017/S1352465820000442

Parry, G., Bennett, D., Roth, A.D. and Kellett, S. (2020), Developing a competence framework for cognitive analytic therapy. Psychol Psychother Theory Res Pract.

Kellett S, Easton K, Cooper M, Millings A, Simmonds-Buckley M, Parry G (2020) Evaluation of a Mobile App to Enhance Relational Awareness and Change During Cognitive Analytic Therapy: Mixed Methods CaseSeries. JMIR Ment Health 2020;7(12): e19888 URL: doi: 10.2196/19888


S Kellett, J Ghag, K Ackroyd, K Freshwater, J Finch, A Freear, J Hartley & M Simmonds‐Buckley (2019) . Delivering cognitive analytic consultancy to community mental health teams: Initial practice‐based evidence from a multi‐site evaluation.  Psychology and Psychotherapy: Theory Research and Practice. Early View 28 March 2019 (Open Access)

Kellett, S., & Lees, S. (2019). Quasi-experimental N = 1 evaluation of the effectiveness of cognitive analytic therapy for dependent personality disorder. Journal of Psychotherapy Integration. Advance online publication.

Spence C, Kellett S, Totterdell P, Parry G. (2019) Can cognitive analytic therapy treat hoarding disorder? An adjudicated hermeneutic single‐case efficacy design evaluation. Clin Psychol Psychother. 2019; 1–11.


Ryle A. & Kellett, S. (2018). Cognitive Analytic Therapy. Chapter 27 in W.J. Livesley. Handbook of Personality Disorders: Theory, Research and Treatment. NY: Guilford Press. 

Kellett, S. Stockton, C., Marshall, H., Hall, J. Jennings, C., & Degadillo, J. (2018). Efficacy of narrative reformulation during cognitive analytic therapy for depression: randomized dismantling trial. Journal of Affective Disorders, 239, 37-47.

Curling, l., Kellett, S., & Totterdell, P. (2018). Cognitive analytic therapy for obsessive morbid jealousy: a case series. Journal of Psychotherapy Integration, 28, 537-555.

Curling L. , Kellett, S., Totterdell, P., Parry, G., Hardy, G., & Berry, K. (2018). Treatment of obsessive morbid jealousy with cognitive analytic therapy: An adjudicated hermeneutic single-case efficacy design evaluation. Psychology and Psychotherapy; Theory, Research and Practice, 91, 95-116.

Kellett, S., Hall, J., & Compton-Dickinson, S. (2018). Group cognitive analytic music therapy: a quasi-experimental feasibility study conducted in a high secure hospital. Nordic Journal of Music Therapy, doi: 10.1080/08098131.2018.1529697


Evans, M., Kellett, S., Heywood, S., Hall, J., & Majid, S. (2017). Cognitive analytic therapy for bipolar disorder: A pilot randomized controlled trial. Clinical Psychology and Psychotherapy, 24, 22-35.

Sandhu SK, Kellett S & Hardy G (2017) The development of a change model of “exits” during cognitive analytic therapy for the treatment of depression. Clinical Psychology and Psychotherapy 0, pp 1 – 11

Meadows, J. & Kellett, S. (2017) Development and Evaluation of Cognitive Analytic Guided Self-Help (CAT-SH) for Use in IAPT Services. Behavioural & Cognitive Psychotherapy, 45, pp 266 – 284


Berrios, R., Kellett, S., Fiorani, C., & Poggioli, M. (2016). Assessment of identity disturbance: Factor Structure and validation of the Personality Structure Questionnaire (PSQ) in an Italian sample. Psychological Assessment, 28, 27-35

Kellett, S. & Bennett, D. (2016) Integration of competency assessment into CAT supervision: A practical guide.  Chapter 11, pp 149 – 162 in D Pickvance (ed) (2016) Cognitive Analytic Supervision: A relational approach.  Routledge

Kellett S, Simmonds-Buckley M & Totterdell P (2016) Testing the Effectiveness of Cognitive Analytic Therapy for Hypersexuality Disorder: An Intensive Time-Series Evaluation. Journal of Sex & Marital Therapy pp 501 – 516


Calvert, R., Kellett, S., & Hagan, T. (2015). Group cognitive analytic therapy for female survivors of childhood sexual abuse. British Journal of Clinical Psychology, 54, 391-413 

Kerr, I. & Kellett, S. (2015) In S Palmer (ed) The Beginners Guide to Counselling & Psychotherapy. Cognitive Analytic Therapy.  Chapter 20, 265 – 278


Kellett, S. Wilbram, M., Davis, C. & Hardy, G. (2014). Team consultancy using cognitive analytic therapy: a controlled study in assertive outreach. Journal of Psychiatric and Mental Health Nursing, 21, 687-97

Kellett, S. & Hardy, G. (2014). The treatment of Paranoid Personality Disorder with CAT: A mixed methods single case experimental design. Clinical Psychology and Psychotherapy, 21, 452-64

Ryle, A. Kellett, S. Hepple, J. & Calvert, R. (2014). Cognitive analytic therapy at 30. Advances in Psychiatric Treatment, 20, 258 – 268

Calvert, R & Kellett, S. (2014). Cognitive analytic therapy: A review of the outcome evidence base for treatment. Psychology and Psychotherapy; Theory, Research and Practice, 87, 253-77


Kellett, S. & Totterdell, P. (2013). Taming the green-eyed monster: temporal responsivity to cognitive behavioural and cognitive analytic therapy for morbid jealousy. Psychology and Psychotherapy; Theory, Research and Practice, 39, 52-69

Kellett, S. Bennett, D. Ryle, A. & Thake, A. (2013). Cognitive Analytic Therapy for Borderline Personality Disorder: Therapist competence and therapeutic effectiveness in routine practice. Clinical Psychology and Psychotherapy, 20, 216-225


Kellett, S. (2012). In Feltham, C. & Horton, I. The SAGE Handbook of Counselling and Psychotherapy (third edition). Cognitive Analytic Therapy (pp 343-350). Sage

Marriott, M. & Kellett, S. (2009). Evaluating a cognitive analytic therapy service; practice-based outcomes and comparisons with person-centred and cognitive-behavioural therapies. Psychology and Psychotherapy; Theory, Research and Practice, 82, 57-82

Kellett, S. (2007). The treatment of Histrionic Personality Disorder with Cognitive Analytic Therapy; a time series evaluation. Psychology and Psychotherapy; Theory, Research and Practice, 80, 389-405

Kellett, S. (2005). The treatment of Dissociative Identity Disorder with Cognitive Analytic Therapy: Experimental evidence of sudden gains. Trauma and Dissociation, 6, 55-81