Clinical Outcomes in Routine Evaluation (CORE-OM)

1. Abstract

The Clinical Outcomes in Routine Evaluation – Outcome Measure (CORE-OM) is a standardized, pan-theoretical, 34-item self-report questionnaire engineered to assess global psychological distress and clinical change within adult psychological therapy and counseling services. Developed in the United Kingdom by the CORE System Group (Barkham et al., 1998, 2001; Evans et al., 2002), the CORE-OM addresses the methodological imperative for a psychometrically rigorous, brief, and ecologically valid instrument tailored to routine outcome monitoring (ROM) and practice-based evidence (PBE). The measure samples four primary dimensions: Subjective Well-being (4 items), Problems/Symptoms (12 items), Life Functioning (12 items), and Risk/Harm (6 items). Respondents evaluate how frequently they have experienced specific affective, somatic, cognitive, relational, and behavioral manifestations over the preceding one-week timeframe utilizing a 5-point Likert scale (0 = Not at all to 4 = Most or all the time).

Extensive psychometric investigations across diverse healthcare environments—including primary care counseling, university mental health clinics, National Health Service (NHS) secondary care, and specialized psychotherapy units—demonstrate exceptional internal consistency (Cronbach’s alpha ranging from .92 to .94 for the total score) and high 24- to 48-hour test-retest reliability ($r = .87$ to $.91$). Convergent validity is evidenced by strong correlations with benchmark clinical measures, such as the Beck Depression Inventory (BDI-II), the Symptom Checklist-90-Revised (SCL-90-R), and the General Health Questionnaire (GHQ-28). Construct and structural validation studies validate both a higher-order general psychological distress factor and distinct multidimensional subscales, with robust sensitivity to therapeutic change that enables precise classification of reliable and clinically significant change via Jacobson and Truax methodologies. Today, the CORE-OM stands as one of the most widely deployed outcome measurement tools internationally, serving as the benchmark foundation for the entire CORE assessment suite.

2. Keywords

Clinical Outcomes in Routine Evaluation, CORE-OM, routine outcome monitoring, psychotherapy outcomes, psychological distress, psychometrics, practice-based evidence, clinical significance, Jacobson-Truax criteria, subjective well-being, risk assessment.

3. Authors

The CORE-OM was designed, refined, and standardized by the CORE System Group, a collaborative team of clinical psychologists, psychotherapy researchers, psychiatrists, and health service methodologists based in the United Kingdom:

• Chris Evans, MD, FRCPsych: Consultant Psychotherapist and Senior Research Fellow at the Tavistock and Portman NHS Foundation Trust; Visiting Professor at the University of Roehampton, London, United Kingdom. Co-founder of the CORE System Trust.
• Janice Connell, PhD: Research Fellow in the Mental Health and Population Research Group, School of Health and Related Research (ScHARR), University of Sheffield, Sheffield, United Kingdom.
• Michael Barkham, PhD, FBPsS: Professor of Clinical Psychology, Centre for Psychological Services Research, Department of Psychology, University of Sheffield, Sheffield, United Kingdom.
• Frank Margison, MD, FRCPsych: Consultant Psychiatrist in Psychotherapy, Gaskell House Psychotherapy Centre, Central Manchester and Manchester Children’s University Hospitals NHS Trust, Manchester, United Kingdom.
• Graeme McGrath, MD, FRCPsych: Consultant Psychiatrist in Psychotherapy, South Manchester University Hospitals NHS Trust, Manchester, United Kingdom.
• John Mellor-Clark, PhD: Director of CORE Information Management Systems (CORE IMS); formerly Senior Research Fellow at the Psychological Therapies Research Centre, University of Leeds, Leeds, United Kingdom.
• Kathy Audin, PhD: Research Officer and Methodologist, Psychological Therapies Research Centre, University of Leeds, Leeds, United Kingdom.

4. Purpose

The development of the Clinical Outcomes in Routine Evaluation – Outcome Measure was catalyzed by a critical paradigm shift in behavioral healthcare during the late 1990s: the transition from isolated, randomized controlled trials (RCTs) toward ecological, practice-based evidence (EBP). While RCTs provide high internal validity regarding manualized interventions in homogeneous cohorts, they frequently lack generalizability across complex, comorbid clinical populations treated in everyday mental health services. To bridge this gap, psychological therapy services required a measurement instrument that was brief, non-intrusive, psychometrically robust, sensitive to therapeutic change, and conceptually neutral across differing therapeutic modalities—including psychodynamic, humanistic, cognitive-behavioral, and integrative orientations.

The primary clinical and operational purposes of the CORE-OM encompass:

• Routine Outcome Monitoring (ROM): Administering the scale at baseline (pre-therapy) and termination (post-therapy) allows clinicians and health service managers to track individual therapeutic progress, measure symptom attenuation, and evaluate overall service effectiveness.
• Session-by-Session Clinical Tracking: In high-frequency configurations, the CORE-OM (and its shortened derivatives, such as the CORE-10 and CORE-SF) is applied longitudinally across sessions to monitor client trajectories, facilitating early detection of non-response, therapeutic rupture, or clinical deterioration.
• Benchmarking and Service Evaluation: The measure offers standardized metrics that enable local, regional, and national psychological services to benchmark treatment effect sizes against established clinical normative datasets, supporting clinical governance and resource allocation.
• Risk Screening and Safeguarding: By isolating dedicated indicators of self-harm, suicidal ideation, and interpersonal violence, the tool serves an immediate triage function, alerting clinicians to escalating clinical emergencies requiring rapid intervention.
• Categorization of Reliable and Clinically Significant Change: Grounded in the statistical framework articulated by Neil S. Jacobson and Paula Truax (1991), the CORE-OM provides precise mathematical cut-off points to classify whether a patient’s trajectory reflects true, reliable improvement beyond measurement error, movement from a dysfunctional to a functional population, or clinically meaningful deterioration.

5. Psychological Construct

The CORE-OM operationalizes psychological distress not as an isolated psychiatric symptom complex, but as a dynamic, systemic, and multi-layered construct. Rather than aligning exclusively with diagnostic taxonomies such as the DSM or ICD, the instrument captures the generalized systemic disruption experienced by an individual across emotional, cognitive, physical, relational, and behavioral domains. The 34 items of the CORE-OM are organized into four theoretical dimensions:

5.1. Subjective Well-being (4 Items)

Subjective well-being denotes the individual’s core baseline evaluation of their own psychological state, life satisfaction, and capacity for self-acceptance. The items assess foundational feelings of self-regard (e.g., “I have felt O.K. about myself”), optimistic prospective outlook (e.g., “I have felt optimistic about my future”), emotional balance, and personal resilience. In psychological distress, subjective well-being is often the first dimension to erode and the final dimension to fully stabilize. High scores (reflecting high distress due to the reversal of positively keyed items) capture states of demoralization, despair, and existential depletion.

5.2. Problems and Symptoms (12 Items)

This domain captures the primary clinical symptoms that motivate individuals to seek psychological intervention. The dimension covers three core symptom clusters:

• Depressive Affect and Cognitive Inhibition: Feelings of unhappiness, pervasive lethargy, crying spells, exhaustion, lack of energy and enthusiasm, and hopelessness (e.g., “I have felt totally lacking in energy and enthusiasm”, “I have felt unhappy”).
• Anxiety, Somatization, and Panic: Hyperarousal, autonomic panic, acute terror, physical somatic disturbances, muscle tension, sleep maintenance insomnia, and somatic aches (e.g., “I have felt panic or terror”, “I have had difficulty getting to sleep or staying asleep”).
• Intrusive Cognition and Traumatic Stress: The intrusion of distressing, unwanted thoughts, painful mental imagery, flashbacks, and cognitive rumination (e.g., “Unwanted images or memories have been distressing me”).

5.3. Life Functioning (12 Items)

Psychological distress inevitably impairs an individual’s capacity to navigate the demands of daily life. The life functioning domain evaluates social, relational, and occupational adaptation across three interpersonal tiers:

• General and Occupational Functioning: The ability to complete necessary daily obligations, executive productivity, coping with unexpected stressors, and experiencing agency (e.g., “I have been able to do most things I needed to”, “I have felt able to cope when things go wrong”).
• Close, Intimate Relationships: The capacity to express and receive interpersonal warmth, affection, perceived social support, and interpersonal trust (e.g., “I have felt warmth or affection for someone”, “I have felt I have someone to turn to for support when needed”).
• Social and Community Interaction: Feelings of marginalization, social isolation, alienation, communicative avoidance, and social irritability (e.g., “I have felt terribly alone and isolated”, “Talking to people has felt too much for me”).

5.4. Risk and Harm (6 Items)

The risk dimension is a crucial clinical feature of the CORE-OM, deliberately isolating critical behaviors and cognitions that require safeguarding attention. Unlike the other dimensions, which assume continuous normal-to-clinical distributions, risk items often show severe positive skew in primary care populations. The domain is bifurcated into:

• Risk to Self (4 Items): Explicit suicidal intent, ideation of death, active suicide planning, direct self-injurious behavior, and dangerous health risk-taking (e.g., “I made plans to end my life”, “I have thought of hurting myself”, “I have thought it would be better if I were dead”).
• Risk to Others (2 Items): Aggressive outward behavioral dysregulation, verbal intimidation, threatening behaviors, and overt physical violence toward other individuals (e.g., “I have threatened or intimidated another person”, “I have been physically violent to others”).

6. Theoretical Framework

The CORE-OM is grounded in contemporary clinical psychometrics, service delivery models, and psychotherapy change theory. It integrates three prominent conceptual frameworks:

6.1. The Phase Model of Psychotherapy Outcome

The conceptual blueprint of the CORE-OM aligns with the tri-phasic model of psychotherapeutic change formulated by Kenneth I. Howard and colleagues (1993). Howard’s model posits that successful psychological therapy unfolds across three sequential stages:

1. Remoralization: The restoration of subjective well-being, perceived self-efficacy, and hope, typically observed within the initial sessions of therapy. This matches the CORE-OM Subjective Well-being domain.
2. Remediation: The progressive reduction and resolution of targeted clinical symptoms and distressing acute phenomena, representing the intermediate phase of therapy. This maps onto the CORE-OM Problems/Symptoms domain.
3. Rehabilitation: The restoration of long-term social, occupational, and interpersonal life functioning, unlearning unhelpful coping strategies and cultivating sustained resilience. This corresponds to the CORE-OM Life Functioning domain.

By mapping its assessment domains to these phases, the CORE-OM enables clinicians to observe whether client change progresses along these predictable trajectories.

6.2. Practice-Based Evidence (PBE) and Routine Healthcare Science

Traditional psychiatric measurement instruments are frequently criticized for poor fit within routine clinical workflows; they are often too narrow (targeting single diagnostic categories like major depression or generalized anxiety) or too burdensome for routine pre- and post-session delivery. The theoretical ethos underpinning the CORE system, as articulated by Barkham and colleagues (2001, 2010), prioritizes Practice-Based Evidence. PBE asserts that real-world clinical data, gathered continuously within routine, unselected clinical populations across diverse clinical styles, is essential for demonstrating treatment validity. Consequently, the CORE-OM was designed to be pan-theoretical—equally valid when evaluating cognitive-behavioral therapies, psychodynamic psychotherapy, systemic family therapy, or person-centered counseling.

6.3. The Dose-Response and Change-Tracking Paradigms

Drawing on the dose-response relationship in mental health interventions (Hansen et al., 2002), the CORE-OM conceptualizes psychological improvement as a non-linear, individualized process. The scale provides the measurement precision needed to compute the Reliable Change Index (RCI) and determine Clinically Significant Change (CSC) (Jacobson & Truax, 1991). This allows practitioners to distinguish between minor measurement fluctuations and statistically verified therapeutic transformation.

7. Validity

The CORE-OM has undergone extensive empirical validation across outpatient psychotherapy services, primary care mental health networks, inpatient psychiatric wards, higher education student counseling centers, and prison health facilities.

7.1. Convergent and Criterion Validity

In the seminal psychometric validation study conducted by Evans et al. (2002) with clinical ($N = 890$) and non-clinical ($N = 1,106$) cohorts, the CORE-OM demonstrated high convergent validity against established standardized instruments:

• Beck Depression Inventory (BDI-II): Total CORE-OM scores correlate strongly with BDI-II scores ($r = .75$ to $.85$), with the CORE-OM Problems subscale demonstrating particularly high concordance ($r = .84$).
• Symptom Checklist-90-Revised (SCL-90-R): Strong positive correlations are observed with the Global Severity Index (GSI) of the SCL-90-R ($r = .80$ to $.88$), confirming that the CORE-OM captures core psychiatric distress.
• General Health Questionnaire (GHQ-28): Correlations between the CORE-OM and GHQ-28 total score range from $.72$ to $.79$.
• Short Form Health Survey (SF-36): Negative correlations are consistently documented with the SF-36 Mental Health Index ($r = -.70$ to $-.78$), demonstrating construct alignment with health-related quality of life.

7.2. Discriminant and Known-Groups Validity

The CORE-OM demonstrates high discriminant validity, distinguishing between clinical populations seeking psychological treatment and asymptomatic community controls. Evans et al. (2002) observed significant mean score differences between non-clinical cohorts (Mean $= 0.48$, $SD = 0.41$) and clinical cohorts awaiting intervention (Mean $= 1.83$, $SD = 0.67$), yielding an effect size (Cohen’s $d$) exceeding $2.4$. The instrument also distinguishes between outpatients in secondary care and primary care counseling clients, accurately reflecting differences in psychological severity.

7.3. Sensitivity to Change and Responsiveness

The scale shows marked responsiveness to therapeutic change. Pre- to post-treatment assessments across multi-site clinical audits reveal large within-group effect sizes (Cohen’s $d$ typically ranging between $1.00$ and $1.45$ for completed therapies). Benchmarking research confirms that the non-risk items (CORE-NR) are especially responsive to psychotherapeutic interventions, whereas the risk items provide essential safeguarding metrics that track symptom crises.

8. Reliability

The reliability of the CORE-OM has been confirmed across clinical settings, general population surveys, and cross-cultural adaptations.

8.1. Internal Consistency

Extensive studies report high internal consistency for the total score and its constituent subscales. Cronbach’s alpha coefficients and McDonald’s omega estimates consistently surpass standard psychometric thresholds across clinical and non-clinical samples:

• Total Score (34 Items): Demonstrates an overall Cronbach’s alpha of $\alpha = .94$ in clinical samples and $\alpha = .92$ in non-clinical samples (Evans et al., 2002; Barkham et al., 2005).
• Subjective Well-being Subscale (4 Items): Displays internal consistency ranging from $\alpha = .75$ to $.82$.
• Problems/Symptoms Subscale (12 Items): Consistently demonstrates $\alpha = .88$ to $.91$.
• Life Functioning Subscale (12 Items): Yields $\alpha = .84$ to $.88$.
• Risk/Harm Subscale (6 Items): Demonstrates $\alpha = .75$ to $.79$. The slightly lower alpha on this subscale reflects its clinical structure: risk to self and risk to others are relatively distinct clinical concerns, combined with the low base-rate endorsement of violence in typical outpatient samples.
• CORE Non-Risk Score (CORE-NR, 28 Items): Exhibits high internal consistency with $\alpha = .93$ to $.95$.

8.2. Test-Retest Reliability

Test-retest stability was investigated by Evans et al. (2002) in a non-clinical student sample across intervals of 24 to 48 hours to minimize true clinical drift while controlling for recall memory. Intraclass correlation coefficients and Pearson correlations confirmed high stability:

• Total Score: $r = .88$ to $.91$
• Subjective Well-being: $r = .84$
• Problems/Symptoms: $r = .87$
• Life Functioning: $r = .83$
• Risk/Harm: $r = .78$

Over a two-week interval without intervention, stability coefficients remain solid ($r = .75$ to $.83$), confirming the scale’s stability in the absence of treatment alongside its sensitivity to change when therapy occurs.

9. Factor Analysis

The internal structural validity of the CORE-OM has been evaluated using both Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA), sparking important discussions in the psychometric literature.

9.1. Exploratory Factor Structure

During the initial development of the scale (Evans et al., 2002), exploratory factor analyses identified a dominant primary factor accounting for a large proportion of common variance—representing General Psychological Distress. When secondary factors were extracted, items clustered meaningfully around the conceptually proposed domains of Problems/Symptoms, Subjective Well-being, Life Functioning, and Risk.

9.2. Confirmatory Factor Analysis and Structural Models

Subsequent structural evaluations (e.g., Lyne et al., 2006; Bedford et al., 2010) examined multiple competing models to determine whether the CORE-OM is best represented as unidimensional, multidimensional, or hierarchical:

• Four-Factor Correlated Model: Evaluates the four original dimensions (Well-being, Problems, Functioning, Risk). Although this model demonstrates acceptable goodness-of-fit indices (Comparative Fit Index [CFI] $\approx .90$, Root Mean Square Error of Approximation [RMSEA] $\approx .055$), high inter-factor correlations between Well-being, Problems, and Functioning ($r > .80$) suggest substantial shared variance.
• Second-Order Hierarchical Model: Posits that a general distress factor accounts for the shared variance among the first-order factors of Well-being, Problems, and Functioning, with Risk loading distinctly. This model yields acceptable fit and aligns with clinical utility.
• Bifactor Model: Recent structural evaluations (e.g., O’Shea et al., 2016) demonstrate that a bifactor model often provides superior statistical fit (CFI $> .95$, Tucker-Lewis Index [TLI] $> .94$, RMSEA $< .045$). In this model, every item loads directly onto a general “General Psychological Distress” factor ($G$), while residual variances cluster onto group factors corresponding to Life Functioning, Specific Symptoms, and Risk.

Item Loadings and the Risk Factor: Across CFA investigations, non-risk items (Well-being, Symptoms, Functioning) show high loadings on the general distress factor (ranging from $.50$ to $.82$). Conversely, the Risk items load distinctly on their dedicated subscale, supporting the practice of evaluating Risk both as a separate clinical safety index and as part of the overall composite score.

10. Instrument / Measurement Tool

• Instrument Name: Clinical Outcomes in Routine Evaluation – Outcome Measure (CORE-OM)
• Instrument Type: Self-administered, standardized clinical rating scale / patient-reported outcome measure (PROM)
• Target Population: Adults (aged 18 to 65+ years) receiving psychological interventions, psychotherapy, or psychiatric services. (Specialized adaptations exist for younger cohorts [CORE-YP] and individuals with intellectual disabilities [CORE-LD]).
• Administration Time: Approximately 5 to 10 minutes.
• Item Count: 34 items.
• Dimensional Structure:
  • Subjective Well-being (4 items: 4, 14, 17, 31)
  • Problems/Symptoms (12 items: 2, 5, 8, 11, 13, 15, 18, 20, 23, 27, 28, 30)
  • Life Functioning (12 items: 1, 3, 7, 10, 12, 19, 21, 25, 26, 29, 32, 33)
  • Risk/Harm (6 items: 6, 9, 16, 22, 24, 34)
  • Non-Risk Composite (CORE-NR): 28 items (combining Well-being, Problems, and Functioning).
• Authentic Response Scale: 5-point Likert scale:
  • 0 = Not at all
  • 1 = Only occasionally
  • 2 = Sometimes
  • 3 = Often
  • 4 = Most or all the time
• Scoring and Transformation Protocols:
  • Positively Keyed (Healthy) Items: Eight items express positive functioning and must be reverse-scored prior to aggregation: Items 3, 4, 7, 12, 19, 21, 31, and 32 (transformed as $0 to 4$, $1 to 3$, $2 to 2$, $3 to 1$, $4 to 0$).
  • Total Raw Score: Calculated as the direct sum of all 34 scored items (range: 0 to 136).
  • Mean Item Score (Clinical Score): Widely used in international literature; computed by dividing the total raw score by the number of completed items (range: 0.0 to 4.0), or multiplied by 10 to yield a 0 to 40 clinical metric.
  • Domain Mean Scores: The sum of domain items divided by the number of completed items within that domain.
  • Missing Data Rule: If three or fewer items are missing on the 34-item form, the mean of the completed items within the respective domain may be imputed. If four or more items are omitted, the total score should be treated as invalid. Missing risk items must not be imputed and require direct clinical review.
• Clinical Thresholds and Cut-Off Scores:
  • Clinical Cut-off (Non-clinical vs. Clinical): A mean item score of approximately 1.00 (or a clinical score of 10.0) demarcates the functional from the dysfunctional distribution in UK adult normative datasets.
  • Distress Bands (Mean Score / 10-point scale):
    • Healthy / Non-clinical: 0.0 – 0.99 (0 – 9.9)
    • Low Psychological Distress: 1.0 – 1.49 (10 – 14.9)
    • Mild Psychological Distress: 1.5 – 1.99 (15 – 19.9)
    • Moderate Psychological Distress: 2.0 – 2.49 (20 – 24.9)
    • Moderate-to-Severe Distress: 2.5 – 2.99 (25 – 29.9)
    • Severe Psychological Distress: $ge 3.0$ ($ge 30.0$)
  • Reliable Change Index (RCI): A change of $ge 0.50$ in the mean score (or $ge 5.0$ on the 0–40 clinical score, representing 17 raw score points) indicates statistically reliable therapeutic change at the $p < .05$ level that cannot be attributed to measurement unreliability.

11. Permissions & Fee and Test Year

• Original Year of Publication: 1998 (initial field implementation and operational user guide); definitive psychometric peer-reviewed publication published in 2002.
• Authors and Copyright Holders: The CORE System Group; copyright administered internationally by the CORE System Trust (a registered not-for-profit educational charity in the United Kingdom).
• Licensing and Fee Structure: The CORE-OM is distributed under an “open access” / Creative Commons philosophy for clinical and research practice. Paper-and-pencil copies may be downloaded, reproduced, and administered free of financial charge, provided no modifications are made to the wording, scoring, or response format, and the official copyright acknowledgement is preserved.
• Commercial Software and Electronic Implementation: While the measure is freely available for paper administration, commercial health systems, software developers, and electronic health record (EHR) platforms incorporating the CORE-OM or its sister tools (e.g., CORE-10, CORE-SF, CORE-YP) into proprietary systems must secure formal licensing and certification agreements via CORE IMS or the CORE System Trust (www.coresystemtrust.org.uk).

12. References

• Barkham, M., Evans, C., Margison, F., McGrath, G., Mellor-Clark, J., Milne, D., & Connell, J. (1998). The rationale for developing and negotiating the Core battery of psychological therapy outcome measures. Journal of Mental Health, 7(3), 247–253. https://doi.org/10.1080/09638239818074
• Barkham, M., Margison, F., Leach, C., Lucock, M., Mellor-Clark, J., Evans, C., Benson, L., Connell, J., Audin, K., & McGrath, G. (2001). Service profiling and benchmark end-of-treatment outcomes for psychological therapies in the NHS: The CORE System. The British Journal of Psychiatry, 178(3), 257–266. https://doi.org/10.1192/bjp.178.3.257
• Barkham, M., Gilbert, N., Connell, J., Marshall, C., & Twigg, E. (2005). Suitability and utility of the CORE-OM and CORE-A for assessing severity of presenting problems and treatment outcomes in primary care. British Journal of Guidance & Counselling, 33(4), 519–536. https://doi.org/10.1080/03069880500327530
• Barkham, M., Hardy, G. E., & Mellor-Clark, J. (Eds.). (2010). Developing and delivering practice-based evidence in healthcare: The CORE system in practice. John Wiley & Sons. https://doi.org/10.1002/9780470684795
• Bedford, A., Watson, R., Lyne, J., & Davies, F. (2010). A psychometric evaluation of the CORE-OM in a UK outpatient clinical population. Clinical Psychology & Psychotherapy, 17(5), 448–453. https://doi.org/10.1002/cpp.678
• Connell, J., Barkham, M., Stiles, W. B., Twigg, E., Singleton, N., Evans, O., & Miles, J. N. (2007). Distribution of CORE-OM scores in a general population, clinical and student samples. Psychology and Psychotherapy: Theory, Research and Practice, 80(3), 331–353. https://doi.org/10.1348/147608306X154089
• Evans, C., Connell, J., Barkham, M., Margison, F., McGrath, G., Mellor-Clark, J., & Audin, K. (2002). Towards a standardised brief outcome measure: Psychometric properties and utility of the CORE-OM. The British Journal of Psychiatry, 180(1), 51–60. https://doi.org/10.1192/bjp.180.1.51
• Hansen, N. B., Lambert, M. J., & Forman, E. M. (2002). The psychotherapy dose-response effect and its implications for treatment delivery services. Clinical Psychology: Science and Practice, 9(3), 329–343. https://doi.org/10.1093/clipsy.9.3.329
• Howard, K. I., Lueger, R. J., Maling, M. S., & Martinovich, Z. (1993). A phase model of psychotherapy outcome: Empirical and clinical advances. Journal of Consulting and Clinical Psychology, 61(4), 678–685. https://doi.org/10.1037/0022-006X.61.4.678
• Jacobson, N. S., & Truax, P. (1991). Clinical significance: A statistical approach to defining meaningful change in psychotherapy research. Journal of Consulting and Clinical Psychology, 59(1), 12–19. https://doi.org/10.1037/0022-006X.59.1.12
• Lyne, K. J., Barrett, P., Evans, C., & Barkham, M. (2006). Dimensions of variation on the PC-SCL-90-R and the CORE-OM: An evaluation of their factor structure and measurement invariance. Psychology and Psychotherapy: Theory, Research and Practice, 79(3), 429–449. https://doi.org/10.1348/147608305X70051
• O’Shea, G., Spence, S. H., & Donovan, C. L. (2016). Structural validity of the CORE-OM: A bifactor model. Psychological Assessment, 28(8), 940–951. https://doi.org/10.1037/pas0000228

13. Items of the Scale