Fatigue Questionnaire (CIS 20R)

Abstract

The Checklist Individual Strength (CIS-20R), widely documented in scientific literature as the Fatigue Questionnaire (CIS 20R), is an internationally validated, multidimensional self-report instrument designed to assess the severity, qualitative features, and behavioral manifestations of persistent fatigue over a two-week recall period. Originally developed by Jan H. M. M. Vercoulen and colleagues at the Radboud University Nijmegen Medical Centre and subsequently psychometrically standardized across occupational and general populations by Beurskens et al., the instrument was constructed to address the psychometric limitations of unidimensional fatigue measures. The CIS-20R comprises 20 items evaluated on a 7-point Likert response scale anchored from 1 (“yes, that is true”) to 7 (“no, that is not true”). Psychometric investigations consistently corroborate a robust four-factor latent structure encompassing: (1) Subjective Feeling of Fatigue (8 items), reflecting the core phenomenological sensation of exhaustion and physical depletion; (2) Reduced Concentration (5 items), evaluating cognitive processing difficulties and executive mental fatigue; (3) Reduced Motivation (4 items), tapping intrinsic drive, initiation, and goal-directed hedonic tone; and (4) Reduced Physical Activity (3 items), measuring functional behavioral throughput and daily activity levels.

Extensive psychometric evaluations establish high internal consistency across diverse clinical and non-clinical cohorts, with Cronbach’s alpha coefficients routinely exceeding α = 0.88 for the Subjective Fatigue subscale and α = 0.90 for the aggregated composite score. Test-retest reliability across stable intervals ranges from r = 0.74 to 0.86, confirming measurement temporal stability. The instrument demonstrates robust convergent validity with functional impairment markers, such as the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) Vitality subscale, and discriminant validity against primary psychopathological constructs of major depression and generalized anxiety. Widely deployed in clinical trials for Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS), post-cancer fatigue, multiple sclerosis, and occupational epidemiology, the CIS-20R provides distinct cutoff thresholds (e.g., a score of ≥ 35 on the Subjective Fatigue subscale) that serve as clinical benchmarks for identifying severe, debilitating fatigue and monitoring therapeutic responsiveness.

Keywords

Checklist Individual Strength, CIS-20R, Fatigue Questionnaire, subjective fatigue, cognitive fatigue, reduced motivation, physical activity, chronic fatigue syndrome, occupational fatigue, psychometrics

Authors

The Checklist Individual Strength was originally conceptualized, operationalized, and clinically validated by research teams based in the Netherlands, primarily associated with the Department of Medical Psychology at Radboud University Nijmegen Medical Centre (formerly Catholic University of Nijmegen) and the Department of Occupational Health and Epidemiology at Maastricht University.

• Jan H. M. M. Vercoulen, Ph.D. — Principal developer; Clinical Psychologist and Psychometrician, Department of Medical Psychology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands. Key contributor to cognitive-behavioral paradigms of chronic fatigue and empirical operationalization of multi-attribute exhaustion.
• Gijs Bleijenberg, Ph.D. — Professor Emeritus of Medical Psychology and former Director of the Expert Centre Chronic Fatigue (ECCF), Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands. Renowned for longitudinal research into the maintenance mechanisms of chronic fatigue and randomized clinical trials of cognitive behavioral therapy.
• Caroline M. A. Swanink, M.D., Ph.D. — Department of Medical Microbiology, Radboud University Nijmegen Medical Centre; collaborator in physiological, immunological, and biological validation studies of prolonged fatigue states.
• Jurgen F. M. Fennis, M.D., Ph.D. — Department of General Internal Medicine, Radboud University Nijmegen Medical Centre; focused on clinical differentiations between somatic disease-associated fatigue and functional fatigue syndromes.
• Jos W. M. van der Meer, M.D., Ph.D. — Professor of Medicine, Department of Internal Medicine, Radboud University Nijmegen Medical Centre; pioneering investigator in internal medicine, infectious diseases, and the etiology of post-infectious fatigue syndromes.
• A. J. (Sandra) Beurskens, Ph.D. — Department of Health Services Research, Maastricht University, and Zuyd University of Applied Sciences, Heerlen, the Netherlands. Lead investigator of the landmark occupational validation study establishing normative parameters, factorial invariance, and cut-off points in working populations (Beurskens et al., 2000).
• Ute Bültmann, Ph.D. — Department of Epidemiology, Maastricht University; currently Professor of Work and Health, University of Groningen, the Netherlands. Expert on prospective occupational cohort tracking, sickness absence, and work-related psychosocial fatigue.
• Ijmer Kant, Ph.D. — Associate Professor of Occupational Epidemiology, Department of Epidemiology, CAPHRI Care and Public Health Research Institute, Maastricht University. Principal architect of the Maastricht Cohort Study on Fatigue at Work.
• Gerard M. H. Swaen, Ph.D. — Senior Epidemiologist, Department of Epidemiology, Maastricht University; investigator in long-term observational designs evaluating occupational determinants and health sequelae of chronic prolonged exhaustion.

Purpose

The Checklist Individual Strength (CIS-20R) was constructed to solve a pervasive diagnostic, conceptual, and psychometric dilemma within medical psychology, psychosomatic medicine, and occupational health: the non-differentiation of acute, restorative exhaustion from prolonged, maladaptive, and multidimensional fatigue. While physiological tiredness is an adaptive, homeostatic signal prompting rest, chronic fatigue represents an incapacitating syndrome characterized by a disproportionality between metabolic exertion and perceived exhaustion, persistent executive cognitive sluggishness, depleted motivational drive, and substantial behavioral functional decline.

Prior to the introduction of the CIS, available clinical scales frequently conflated fatigue with general depressive symptomatology, somatic comorbidity, sleep architecture disturbances, or functional disability scales (such as the Karnofsky Performance Status). Such conflation introduced severe confounding into etiology-seeking research and therapeutic intervention evaluations. The CIS-20R was explicitly designed to isolate fatigue as a distinct, multi-layered construct. By assessing experiences across the preceding two weeks (“during the past two weeks”), the scale establishes an optimal temporal window that balances state-level situational variability against trait-like clinical stability, effectively capturing sustained functional disturbance while retaining sensitivity to longitudinal change.

In clinical practice, the primary purpose of the CIS-20R is the formal identification, baseline stratification, and outcome assessment of individuals suffering from severe fatigue syndromes, including Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS), post-cancer fatigue (PCF), Multiple Sclerosis (MS), post-infectious sequelae (including post-acute COVID-19 condition), and rheumatologic conditions such as systemic lupus erythematosus and rheumatoid arthritis. The scale enables clinicians to determine whether a patient cross-sectionally exceeds empirically established cutoffs for clinical fatigue (e.g., scoring ≥ 35 on the Subjective Fatigue subscale), a threshold validated as separating fully functioning healthy controls from individuals impaired by chronic debilitating fatigue.

In occupational health and organizational psychology, the CIS-20R serves as an epidemiological and surveillance instrument to quantify psychological strain, predict long-term sickness absence, and assess burn-out vulnerability. In the renowned Maastricht Cohort Study, which monitored over 12,000 employees longitudinally, baseline elevations on the CIS subscales demonstrated high predictive utility for incipient psychological morbidity, elevated accident frequency, presenteeism, and prolonged job disengagement. In clinical trials, the scale serves as a standardized primary or secondary endpoint to measure the therapeutic efficacy of behavioral, physical, and pharmacological interventions, documenting whether clinical trials succeed in returning patients to normative population parameters.

Psychological Construct

Fatigue is not an elemental, unitary subjective experience; it is an elaborate, homeostatically driven psychobiological symptom complex encompassing emotional, physiological, cognitive, and behavioral spheres. The theoretical foundation of the CIS-20R is grounded in a multidimensional conceptualization that decomposes fatigue into four distinct yet interconnected operational dimensions:

1. Subjective Feeling of Fatigue (8 Items)

The Subjective Feeling of Fatigue dimension captures the core phenomenological sensation of exhaustion, physical depletion, and pervasive weariness. It measures the qualitative severity of the feeling state rather than the behavioral consequence. Items in this subscale (Items 1, 4, 6, 9, 12, 14, 16, 20) evaluate both direct feelings of exhaustion (“I feel tired”, “Physically I feel exhausted”, “I feel weak”, “I get tired very quickly”) and the inverse states of vitality, vigor, and physical preservation (“I feel fit”, “I feel rested”, “Physically I feel in a good shape”). This subscale represents the primary clinical axis of the CIS-20R, directly tracking the intensity of systemic exhaustion that fails to remit following customary periods of sleep or muscular rest.

2. Reduced Concentration (5 Items)

The Reduced Concentration dimension focuses on the neuropsychological and cognitive manifestations of fatigue, frequently referred to in clinical cohorts as mental fatigue or “brain fog.” This dimension isolates deficits in sustained attention, working memory allocation, executive control, and the subjective effort required to engage in information processing. Items assigned to this factor (Items 3, 8, 11, 13, 19) assess cognitive friction and mental drift (“Thinking requires effort”, “I have trouble concentrating”, “My thoughts easily wander”) alongside self-perceived cognitive competence (“When I am doing something, I can concentrate quite well”, “I can concentrate well”). In psychiatric and post-viral cohorts, this domain often diverges from objective physical fatigue, highlighting selective impairments in neurocognitive resource allocation.

3. Reduced Motivation (4 Items)

The Reduced Motivation dimension taps the affective, hedonic, and volitional elements of fatigue, specifically capturing goal initiation, abulia, and anhedonic lethargy. Prolonged fatigue frequently disrupts the dopaminergic reward-processing networks that translate physiological energy into intentional action. The items within this subscale (Items 2, 5, 15, 18) explore the respondent’s intrinsic motivation, behavioral appetitive drive, and programmatic planning (“I feel very active”, “I feel like doing all kinds of nice things”, “I am full of plans”, “I feel no desire to do anything”). Importantly, psychometric analyses indicate that while this factor correlates with motivational loss seen in major depressive disorder, it captures a distinct construct characterized by an intentional barrier secondary to energetic depletion rather than global affective despair.

4. Reduced Physical Activity (3 Items)

The Reduced Physical Activity dimension assesses the explicit behavioral manifestations and real-world functional throughput resulting from energetic limitation. Rather than indexing subjective physical capability, it records the empirical decline in behavioral output and task execution throughout the waking day. Comprising items 7, 10, and 17 (“I do quite a lot within a day”, “I don’t do much during the day”, “I have a low output”), this subscale provides an ecological bridge between psychological exhaustion and behavioral limitation. In validation studies, this dimension exhibits modest to moderate correlations with actigraphy-derived daily movement counts, reflecting how patients alter their behavioral trajectories to accommodate persistent exhaustion.

Theoretical Framework

The Checklist Individual Strength is historically and conceptually rooted in the Cognitive-Behavioral Model of Chronic Fatigue, pioneered by Vercoulen, Bleijenberg, and colleagues at the Nijmegen school of medical psychology. This theoretical architecture posits that while the initiation of severe fatigue is frequently precipitated by acute biological events (such as viral infections, physiological trauma, neuroendocrine perturbation, or severe episodic psychosocial stress), its persistence, chronification, and functional severity are maintained by an intricate network of cognitive, emotional, behavioral, and interpersonal feedback loops.

According to this cognitive-behavioral model, chronic fatigue syndromes are perpetuated by several distinct maintaining factors:

• Cognitive Attributions and Somatic Hypervigilance: Patients who interpret normative post-exertional bodily sensations as definitive indicators of progressive somatic tissue damage or immunological failure develop somatic hypervigilance. This interpretation drives profound anxiety regarding physical exertion, fostering fear-avoidance behaviors.
• Dysfunctional Activity Patterns: Patients often adopt one of two maladaptive behavioral trajectories: a pervasive avoidant pattern characterized by progressive bed rest, deconditioning, and profound functional withdrawal; or an erratic “all-or-nothing” (boom-and-bust) pattern where individuals overexert themselves on days with marginal symptom relief, subsequently triggering severe symptom flare-ups followed by prolonged periods of physical prostration.
• Neurocognitive Resource Depletion: Incorporating theories of cognitive psychology, such as Daniel Kahneman’s model of attention and effort and subsequent paradigms of executive self-regulation depletion, the framework treats cognitive fatigue as a breakdown in the allocation of central processing resources. When central control systems must continuously monitor bodily symptoms while executing standard tasks, processing capacity is exhausted, manifesting as elevated perceived mental effort and distractibility.
• Disruption of Circadian and Social Rhythms: Inactivity, irregular rest-activity cycles, and the withdrawal of positive environmental reinforcers lead to neuroendocrine blunting (e.g., dysregulation of the hypothalamic-pituitary-adrenal [HPA] axis), impaired restorative sleep, and low social participation, locking the individual into persistent, self-sustaining fatigue.

By decomposing the broad construct of fatigue into subjective sensations, cognitive impairments, motivational states, and overt physical activity levels, the CIS-20R maps directly onto these theoretical maintaining mechanisms. For instance, an individual exhibiting elevated Subjective Fatigue alongside normal Physical Activity presents a markedly different clinical and behavioral profile than an individual showing high Subjective Fatigue paired with extreme Physical Inactivity. The instrument operationalizes these constructs to enable targeted clinical testing of cognitive-behavioral therapy (CBT) and graded exercise therapy (GET), which aim to systematically recalibrate cognitive attributions, stabilize diurnal activity, and resolve avoidant coping mechanisms.

Validity

The validity of the CIS-20R has been empirically demonstrated across hundreds of peer-reviewed investigations spanning occupational epidemiology, psychosomatic medicine, oncology, neurology, and clinical psychology.

Construct and Structural Validity

The construct validity of the CIS-20R was initially established by Vercoulen et al. (1994, 1997) through structural equation modeling and exploratory factor analysis, which established that fatigue cannot be accounted for by a unidimensional latent trait. Confirmatory factor analyses in diverse cohorts consistently support the superior fit of the correlated four-factor model over one-factor, two-factor, or general second-order models. In a foundational validation study conducted on a representative occupational sample of 3,983 employees (Beurskens et al., 2000), the four-factor structure demonstrated exceptional stability across demographic strata (age, sex, educational background) and across longitudinal evaluation waves, confirming measurement invariance.

Convergent Validity

Convergent validity is documented through robust, theoretically congruent associations with alternative validated psychometric instruments. The CIS Subjective Fatigue subscale exhibits strong negative correlations with the Vitality subscale of the SF-36 Health Survey (Pearson r typically ranging between -0.70 and -0.84), reflecting parallel operational coverage of bodily energy depletion. Furthermore, strong positive correlations are observed with corresponding dimensions of the Multidimensional Fatigue Inventory (MFI-20; r = 0.72 to 0.81) and the Chalder Fatigue Questionnaire (CFQ; r = 0.68 to 0.78). The Reduced Concentration subscale correlates significantly with standardized neuropsychological symptom checklists and the Cognitive Failures Questionnaire (CFQ; r = 0.58 to 0.69). The Reduced Physical Activity subscale correlates positively with functional disability indices, including the Sickness Impact Profile (SIP; r = 0.52 to 0.65) and physical functioning limitations on the SF-36 (r = -0.45 to -0.62).

Discriminant and Divergent Validity

The CIS-20R demonstrates strong discriminant validity against core affective disorders. Although fatigue is an established diagnostic criterion for major depressive disorder and generalized anxiety disorder, correlation coefficients between the CIS-20R Subjective Fatigue subscale and validated depression inventories—such as the Beck Depression Inventory (BDI) and the Hospital Anxiety and Depression Scale (HADS-D)—consistently range from r = 0.35 to 0.50. This indicates moderate shared variance (~12-25%) that is attributable to somatic symptom overlap rather than construct redundancy. In ME/CFS and post-cancer cohorts, individuals regularly endorse maximal scores on the CIS Subjective Fatigue subscale while scoring below diagnostic thresholds for depressive mood or anhedonia on the HADS, demonstrating that the CIS-20R does not merely duplicate affective distress.

Criterion and Predictive Validity

Criterion-related validity is evidenced by the scale’s capacity to discriminate between known clinical groups and healthy populations. Mean scores on the Subjective Fatigue subscale in patients diagnosed with ME/CFS according to international consensus criteria average between 45.0 and 52.0 (out of 56), whereas healthy control populations exhibit mean scores ranging from 15.0 to 22.0, yielding substantial effect sizes (Cohen’s d > 2.0). In occupational cohorts, Beurskens et al. (2000) and Bültmann et al. (2000) established that baseline elevated scores on the CIS-20R prospectively predict future sickness absence, long-term work disability, and medical consultations over 12-month follow-up intervals, demonstrating predictive utility in occupational health surveillance.

Reliability

The Checklist Individual Strength (CIS-20R) demonstrates excellent reliability across varied language translations, clinical disorders, and non-clinical workplace cohorts. Metric precision has been examined through internal consistency analyses, test-retest correlations, and intraclass correlation coefficient (ICC) estimations.

Internal Consistency

Internal consistency estimates, quantified via Cronbach’s alpha (α), are consistently high across all four subscales and for the total instrument:

• Subjective Feeling of Fatigue (8 items): Displays the highest internal reliability, with alpha coefficients consistently ranging from α = 0.88 to α = 0.95 across healthy working samples, chronic fatigue syndrome cohorts, multiple sclerosis patients, and cancer survivors.
• Reduced Concentration (5 items): Demonstrates high internal consistency, with alpha coefficients typically between α = 0.82 and α = 0.92.
• Reduced Motivation (4 items): Demonstrates satisfactory internal reliability, with alpha coefficients routinely documented between α = 0.70 and α = 0.86.
• Reduced Physical Activity (3 items): Despite its brief three-item composition, this subscale achieves acceptable internal consistency, with alpha coefficients ranging from α = 0.75 to α = 0.88.
• Total CIS-20R Score: Yields composite internal consistency estimates between α = 0.90 and α = 0.94, confirming strong structural coherence among the pooled items.

Test-Retest Reliability and Temporal Stability

Test-retest reliability assessments across short intervals (e.g., 24 hours to 2 weeks) during which clinical status remains stable demonstrate high temporal consistency. In stable clinical cohorts, intraclass correlation coefficients (ICCs) for the subscales range between 0.74 and 0.86:

• Subjective Fatigue: ICC = 0.81 to 0.86
• Reduced Concentration: ICC = 0.78 to 0.84
• Reduced Motivation: ICC = 0.70 to 0.79
• Reduced Physical Activity: ICC = 0.74 to 0.82

The standard error of measurement (SEM) and smallest detectable change (SDC) metrics indicate that a change of ≥ 7 to 8 points on the Subjective Fatigue subscale represents a statistically reliable and clinically meaningful alteration beyond measurement error at the individual level (Worm-Smeitink et al., 2017).

Factor Analysis

The latent dimensionality of the CIS-20R has been evaluated through exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) across diverse cultural and clinical contexts.

Exploratory Factor Structure

During initial instrument development by Vercoulen et al. (1994), principal component analyses with varimax and oblique rotations were performed on clinical datasets comprising CFS patients and healthy controls. The scree plot and eigenvalue criterion (λ > 1.0) unambiguously isolated four distinct factors accounting for more than 62% of the cumulative variance. Item loadings on their designated target factors were uniformly strong, with primary standardized loadings ranging from 0.52 to 0.87, and cross-loadings on non-target factors remaining low (≤ 0.30). Specifically:

• The primary factor, accounting for the largest proportion of total variance (~38%), was defined by the 8 items evaluating subjective physical and general fatigue.
• The second factor (~11% of variance) clustered the 5 items assessing mental focus, processing effort, and distractibility.
• The third factor (~7% of variance) pooled the 4 items reflecting planning, motivation, and positive behavioral initiative.
• The fourth factor (~6% of variance) encompassed the 3 items measuring behavioral output and physical daily activity.

Confirmatory Factor Analysis (CFA) and Model Fit

Subsequent psychometric evaluations, including the occupational validation study by Beurskens et al. (2000) and clinical validation studies across Europe, utilized CFA to evaluate competing structural models: a unidimensional model, a hierarchical model featuring a general higher-order fatigue factor, and the correlated four-factor model. The correlated four-factor specification consistently yields superior fit indices across goodness-of-fit parameters:

• Comparative Fit Index (CFI): Routinely observed between 0.92 and 0.96 (where values ≥ 0.90 designate acceptable fit, and ≥ 0.95 reflect excellent fit).
• Tucker-Lewis Index (TLI): Typically spans 0.91 to 0.95.
• Root Mean Square Error of Approximation (RMSEA): Consistently falls between 0.048 and 0.065 (90% CI [0.042, 0.071]), confirming acceptable to close approximation error.
• Standardized Root Mean Square Residual (SRMR): Remains low, typically ranging between 0.040 and 0.055.

Standardized factor loadings in CFA models consistently verify strong structural validity. Factor loadings for the Subjective Fatigue items range from 0.62 to 0.88; Concentration items load between 0.58 and 0.85; Motivation items load between 0.51 and 0.79; and Physical Activity items load between 0.66 and 0.86. Moderate inter-factor correlations (ranging from r = 0.38 to 0.65) demonstrate that while these four dimensions share common variance under the broader rubric of exhaustion, they retain discriminant validity as separate subscales.

Instrument / Measurement Tool

The operational characteristics and structural architecture of the Fatigue Questionnaire (CIS-20R) are detailed below:

• Test Type: Multi-dimensional self-report symptom inventory and psychometric rating scale.
• Target Population: Adults and adolescents (≥ 16 years); validated in clinical cohorts (ME/CFS, post-cancer, neurological, rheumatological) and occupational cohorts (general working populations, corporate employees).
• Administration Format: Standard pencil-and-paper or digital, interactive electronic administration. Suitable for individual assessment or large-scale epidemiological survey panels.
• Administration Time: Approximately 5 to 10 minutes.
• Recall Period: Past two weeks (“During the past two weeks…”).
• Item Count: 20 items.
• Response Scale: 7-point Likert rating scale for each item, visually displayed as continuous numbered response anchors:
  
  yes, that is true 1 _ 2 _ 3 _ 4 _ 5 _ 6 _ 7 no, that is not true
• Subscale Breakdown:
  • Subjective Feeling of Fatigue: 8 items (Items 1, 4, 6, 9, 12, 14, 16, 20). Theoretical score range: 8 to 56.
  • Reduced Concentration: 5 items (Items 3, 8, 11, 13, 19). Theoretical score range: 5 to 35.
  • Reduced Motivation: 4 items (Items 2, 5, 15, 18). Theoretical score range: 4 to 28.
  • Reduced Physical Activity: 3 items (Items 7, 10, 17). Theoretical score range: 3 to 21.
  • Total CIS-20R Score: Sum of all four subscale scores. Theoretical score range: 20 to 140.
• Scoring and Directionality Rules:
  • Higher scores across all CIS-20R subscales and for the total scale reflect greater fatigue, lower concentration, lower motivation, and lower physical activity (i.e., greater overall functional impairment).
  • Because the response anchors place 1 at “yes, that is true” and 7 at “no, that is not true”, items indicating impairment are scored in one direction, while items reflecting health, vitality, or high functioning require reverse scoring.
  • Negative Items (indicating fatigue/impairment): Items 1, 3, 4, 9, 10, 13, 14, 16, 17, 18, 19. For these items, endorsing “yes, that is true” (score 1) indicates severe impairment, so they are reverse scored: Score = 8 – Response. (Thus, selecting 1 becomes a score of 7, 2 becomes 6, 3 becomes 5, 4 remains 4, 5 becomes 3, 6 becomes 2, and 7 becomes 1).
  • Positive Items (indicating vitality/functional capacity): Items 2, 5, 6, 7, 8, 11, 12, 15, 20. For these items, endorsing “no, that is not true” (score 7) indicates severe impairment. These items are scored directly as marked: Score = Response. (Thus, selecting 7 corresponds to a score of 7, indicating maximum impairment).
• Clinical and Occupational Cutoff Scores:
  • Subjective Fatigue Subscale:
    • Score ≤ 26: Normal / non-problematic fatigue (typical range for healthy working adults).
    • Score 27 to 34: Heightened / border-zone fatigue; indicates elevated vulnerability to functional impairment or occupational distress.
    • Score ≥ 35: Severe clinical fatigue. This cutoff lies two standard deviations above the mean of healthy populations and represents the standard benchmark for clinical diagnosis, intervention eligibility, and severe functional impairment.
  • Total Score Cutoff: A total score of ≥ 76 is frequently utilized in occupational medicine to designate substantial multi-domain psychological and physical strain.

Permissions & Fee and Test Year

The Checklist Individual Strength was originally developed and published in 1994 by Jan H. M. M. Vercoulen, Gijs Bleijenberg, and colleagues at the Radboud University Nijmegen Medical Centre (Nijmegen, the Netherlands). The revised 20-item version with occupational norming and psychometric standardization (CIS-20R) was published by Sandra A. J. Beurskens and the Maastricht Cohort research group in 2000 in Occupational and Environmental Medicine.

The CIS-20R is an academic, non-commercial assessment instrument. It is generally available free of charge for non-funded academic research, individual educational use, and non-commercial clinical outcome monitoring, provided proper formal bibliographic citation is given to the primary validation literature (Vercoulen et al., 1994; Beurskens et al., 2000). Commercial organizations, funded industrial clinical trials, pharmaceutical studies, and commercial software developers intending to incorporate the CIS-20R into digital health ecosystems or proprietary testing batteries must contact the copyright holders—specifically the Expert Centre Chronic Fatigue (ECCF) at Radboud University Nijmegen Medical Centre—to request licensing terms, translations, and formal permission agreements.

References

• Beurskens, A. J., Bültmann, U., Kant, I., Vercoulen, J. H., Bleijenberg, G., & Swaen, G. M. H. (2000). Fatigue among working people: Validity of a questionnaire measure. Occupational and Environmental Medicine, 57(5), 353–357. https://doi.org/10.1136/oem.57.5.353
• Bültmann, U., de Vries, M., Beurskens, A. J., Bleijenberg, G., Vercoulen, J. H., & Kant, I. (2000). Measurement of prolonged fatigue in the working population: Determination of a cutoff point for the Checklist Individual Strength. Journal of Occupational and Health Psychology, 5(4), 411–416. https://doi.org/10.1037/1076-8998.5.4.411
• Dittner, V. C., Wessely, S. C., & Brown, R. G. (2004). The assessment of fatigue: A practical guide for clinicians and researchers. Journal of Psychosomatic Research, 56(2), 157–170. https://doi.org/10.1016/S0022-3999(03)00371-4
• Vercoulen, J. H. M. M., Swanink, C. M. A., Fennis, J. F. M., Galama, J. M. D., van der Meer, J. W. M., & Bleijenberg, G. (1994). Dimensional assessment of chronic fatigue syndrome. Journal of Psychosomatic Research, 38(5), 383–392. https://doi.org/10.1016/0022-3999(94)90099-X
• Vercoulen, J. H. M. M., Hommes, O. R., Swanink, C. M. A., Jongen, P. J. H., Fennis, J. F. M., Galama, J. M. D., van der Meer, J. W. M., & Bleijenberg, G. (1996). The measurement of fatigue in patients with multiple sclerosis: A multidimensional comparison with patients with chronic fatigue syndrome and healthy subjects. Archives of Neurology, 53(7), 642–649. https://doi.org/10.1001/archneur.1996.00550070080014
• Vercoulen, J. H. M. M., Swanink, C. M. A., Zitman, F. G., Vreden, S. G., Hoofs, M. P., Fennis, J. F. M., Galama, J. M. D., van der Meer, J. W. M., & Bleijenberg, G. (1997). The Checklist Individual Strength (CIS). Gedragstherapie, 30(2), 153–159.
• Worm-Smeitink, M., Gielissen, M., Bloot, L., van Laarhoven, H. W. M., van Engelen, B. G. M., van Riel, P., Bleijenberg, G., Nikolaus, S., & Knoop, H. (2017). The assessment of fatigue: Psychometric qualities and norms for the Checklist Individual Strength. Journal of Psychosomatic Research, 98, 40–46. https://doi.org/10.1016/j.jpsychores.2017.05.007

Items of the Scale