Clinical Psychology — Psychological Assessment, the Limits of Diagnostic Systems, Evidence-Based Treatment and Common Factors

This chapter is general information for learning. It does not replace diagnosis or treatment. If you are thinking about harming yourself, contact your local emergency number or a crisis line right away (in the US, call or text 988).

What is clinical psychology?

Clinical psychology is the field that assesses, understands and treats psychological distress and disorder. The scientist-practitioner model, set out at the 1949 Boulder Conference in the US, established that clinical psychologists should be both scientists who understand and use research and practitioners in the field. Where Chapter 5 looked at how mental disorders are classified, this chapter covers how to assess and how to choose treatment according to evidence.

Engel’s (1977) biopsychosocial model remains the basic framework in clinical work. It holds that even the same depression involves genes and the brain (biological), thoughts and coping (psychological), and relationships and finances (social) together, and assessment and treatment look at all three.

Psychological assessment: what makes a good test

Reliability and validity

• Reliability: does the same person get similar results when measured again (test–retest reliability), do the items measure the same thing (internal consistency), and do raters agree (inter-rater reliability)?
• Validity: does the test measure what it claims to? This includes whether it agrees with related measures (convergent validity) and whether it predicts future outcomes (predictive validity).

A test cannot be valid without reliability, but high reliability doesn’t guarantee validity — like a scale that always reads 2 kg too heavy: consistent, but not accurate.

Types of assessment tools

Tool	Examples	Features
Structured interview	SCID (Structured Clinical Interview for DSM)	Checks diagnostic criteria in a fixed order; high inter-rater agreement
Screening scales	PHQ-9 (depression), GAD-7 (anxiety)	Short and free; widely used for screening and tracking progress (Kroenke, Spitzer & Williams, 2001; Spitzer et al., 2006)
Multiphasic inventory	MMPI-2	Hundreds of items, including validity scales that check response style
Projective tests	Rorschach, Thematic Apperception Test	Interpret responses to ambiguous stimuli; scientific support is disputed

Reviewing projective tests, Lilienfeld, Wood and Garb (2000) concluded that, apart from a few indices, evidence for their reliability and validity is weak — one reason not to treat viral online drawing tests as diagnoses.

Clinical judgement versus statistical prediction

Meehl (1954) made the controversial claim that statistical prediction following a set formula is generally more accurate than experts’ intuitive judgement. A meta-analysis of 136 studies likewise found statistical prediction equal to or better than clinical judgement in most cases (Grove et al., 2000). This doesn’t mean clinical experience is useless; it means judgement should be supplemented with structured tools.

The uses and limits of diagnostic systems

The American Psychiatric Association’s DSM-5-TR (2022) and the World Health Organization’s ICD-11 (in effect from 2022) classify disorders by lists of symptoms and criteria. Their great advantage is a shared language that makes research, treatment and insurance claims possible.

Their limits are clear too.

• Comorbidity: people very often receive several diagnoses at once — a sign that the categories actually overlap.
• Arbitrary thresholds: rules like “five symptoms is a diagnosis, four is not” don’t reflect the continuity of real distress.

This is why dimensional models have been proposed. HiTOP arranges symptoms into broad dimensions such as internalising and externalising, with narrower dimensions beneath (Kotov et al., 2017). The US National Institute of Mental Health’s RDoC is a framework for studying basic functional domains, such as reward processing and threat response, at levels from genes to behaviour (Insel et al., 2010).

Evidence-based treatment

The American Psychological Association (APA, 2006) defined evidence-based practice as the integration of three elements:

1. The best available research evidence
2. Clinical expertise
3. Client characteristics, culture and preferences

Examples of treatments with established efficacy for particular problems (Chambless & Hollon, 1998):

Problem	Well-supported treatments
Panic disorder	CBT (including interoceptive exposure)
Obsessive-compulsive disorder	Exposure and response prevention (ERP)
Depression	Cognitive therapy, behavioural activation, interpersonal therapy
PTSD	Prolonged exposure, cognitive processing therapy, EMDR

In a randomised trial by Dimidjian et al. (2006), behavioural activation — deliberately scheduling more activities that bring pleasure and accomplishment — performed comparably to antidepressants for severe depression. Individual therapies are covered in more detail in understanding psychotherapy through research.

Common factors in therapy

Rosenzweig (1936) likened the observation that different therapies produce similar results to the Dodo bird’s verdict in Alice in Wonderland: “Everybody has won, and all must have prizes.” This later grew into the Dodo bird verdict debate.

• Therapeutic alliance: the degree to which therapist and client agree on goals and tasks and share a bond. A meta-analysis of nearly 300 studies found a correlation of about .28 between alliance and outcome, consistently across therapy types (Flückiger et al., 2018).
• The contextual model: Wampold (2015) argued that common factors such as empathy, expectations and the alliance explain outcomes as much as, or more than, specific techniques.

There are, however, cases where a specific technique is clearly better, such as exposure for OCD, so today the common view is that common factors and specific techniques work together.

Combining medication and psychotherapy

A meta-analysis found that adding psychotherapy to antidepressants for depression and anxiety disorders produced larger effects than medication alone (Cuijpers et al., 2014). Psychotherapy’s effect of reducing relapse after treatment ends also tends to last relatively long. The best combination is decided by weighing symptom severity, past treatment response and personal preference.

Check questions

Question 1. A depression scale gives nearly the same score for the same person two weeks apart, but is almost unrelated to diagnoses from clinical interviews. Evaluate its reliability and validity.

Answer. Its test–retest reliability is high but its validity is low. It measures consistently, but it isn’t properly measuring the depression it is meant to.

Question 2. If two psychotherapies are about equally effective overall, does that mean “it doesn’t matter which treatment you get”?

Answer. No. Similar average effects may reflect common factors, but for certain problems, such as exposure and response prevention for OCD, specific techniques are clearly more effective. You need to consider both the type of problem and the evidence.

Question 3. One person is diagnosed with depression, generalised anxiety disorder and insomnia disorder at the same time. What limitation of categorical diagnostic systems does this show?

Answer. Common comorbidity suggests that disorder categories may actually sit on overlapping dimensions. This is one reason dimensional models such as HiTOP have been proposed.

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References

• Engel, G. L. (1977). The need for a new medical model: A challenge for biomedicine. Science, 196(4286), 129–136.
• Kroenke, K., Spitzer, R. L., & Williams, J. B. W. (2001). The PHQ-9: Validity of a brief depression severity measure. Journal of General Internal Medicine, 16(9), 606–613.
• Spitzer, R. L., Kroenke, K., Williams, J. B. W., & Löwe, B. (2006). A brief measure for assessing generalized anxiety disorder: The GAD-7. Archives of Internal Medicine, 166(10), 1092–1097.
• Lilienfeld, S. O., Wood, J. M., & Garb, H. N. (2000). The scientific status of projective techniques. Psychological Science in the Public Interest, 1(2), 27–66.
• Meehl, P. E. (1954). Clinical versus Statistical Prediction. University of Minnesota Press.
• Grove, W. M., et al. (2000). Clinical versus mechanical prediction: A meta-analysis. Psychological Assessment, 12(1), 19–30.
• American Psychiatric Association (2022). Diagnostic and Statistical Manual of Mental Disorders (5th ed., text rev.).
• World Health Organization (2022). International Classification of Diseases (11th rev.).
• Kotov, R., et al. (2017). The Hierarchical Taxonomy of Psychopathology (HiTOP): A dimensional alternative to traditional nosologies. Journal of Abnormal Psychology, 126(4), 454–477.
• Insel, T., et al. (2010). Research Domain Criteria (RDoC): Toward a new classification framework for research on mental disorders. American Journal of Psychiatry, 167(7), 748–751.
• APA Presidential Task Force on Evidence-Based Practice (2006). Evidence-based practice in psychology. American Psychologist, 61(4), 271–285.
• Chambless, D. L., & Hollon, S. D. (1998). Defining empirically supported therapies. Journal of Consulting and Clinical Psychology, 66(1), 7–18.
• Dimidjian, S., et al. (2006). Randomized trial of behavioral activation, cognitive therapy, and antidepressant medication in the acute treatment of adults with major depression. Journal of Consulting and Clinical Psychology, 74(4), 658–670.
• Rosenzweig, S. (1936). Some implicit common factors in diverse methods of psychotherapy. American Journal of Orthopsychiatry, 6(3), 412–415.
• Flückiger, C., Del Re, A. C., Wampold, B. E., & Horvath, A. O. (2018). The alliance in adult psychotherapy: A meta-analytic synthesis. Psychotherapy, 55(4), 316–340.
• Wampold, B. E. (2015). How important are the common factors in psychotherapy? An update. World Psychiatry, 14(3), 270–277.
• Cuijpers, P., et al. (2014). Adding psychotherapy to antidepressant medication in depression and anxiety disorders: A meta-analysis. World Psychiatry, 13(1), 56–67.