National Institutes of Health-Chronic Prostatitis Symptom Index

1. Abstract

The National Institutes of Health-Chronic Prostatitis Symptom Index (NIH-CPSI) is the globally recognized gold standard patient-reported outcome measure (PROM) designed to evaluate symptom severity and functional impact in men suffering from chronic prostatitis and chronic pelvic pain syndrome (CP/CPPS, Category III). Developed in 1999 by Mark S. Litwin and the Chronic Prostatitis Collaborative Research Network (CPCRN) under the auspices of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the instrument addresses the historical absence of standardized, psychometrically validated indices for male pelvic pain. The NIH-CPSI comprises 9 primary structured questions encompassing 13 individual items organized across three distinct, theoretically cohesive domains: Pain or Discomfort (location, frequency, and severity; items 1–4, scoring 0–21), Urinary Symptoms (irritative and obstructive voiding complaints; items 5–6, scoring 0–10), and Quality of Life Impact (functional impairment, cognitive preoccupation, and life dissatisfaction; items 7–9, scoring 0–12). The total cumulative score ranges from 0 to 43, with higher values reflecting greater symptom burden.

Extensive psychometric investigations across diverse international cohorts have consistently demonstrated robust measurement properties. Internal consistency reliability is high, with Cronbach’s alpha coefficients routinely exceeding α = 0.85 for the total instrument and ranging from α = 0.72 to 0.90 across subscales. Test-retest reliability across stable intervals demonstrates intraclass correlation coefficients (ICCs) between 0.80 and 0.93. Construct, convergent, and discriminant validities are firmly established through strong correlations with the International Prostate Symptom Score (IPSS) and health-related quality of life measures (e.g., SF-12, SF-36), as well as significant discrimination between clinical CP/CPPS populations, asymptomatic controls, and benign prostatic hyperplasia (BPH) cohorts. Confirmatory factor analyses corroborate a robust three-factor latent structure. With an established minimally clinically important difference (MCID) of a 4- to 6-point reduction (or a 25% decrease from baseline), the NIH-CPSI serves as an essential primary endpoint in clinical trials, observational epidemiology, and routine urological and psychological practice worldwide.

2. Keywords

National Institutes of Health-Chronic Prostatitis Symptom Index, NIH-CPSI, chronic pelvic pain syndrome, CP/CPPS, urological chronic pelvic pain, patient-reported outcome measure, psychometrics, pain assessment, urinary dysfunction, health-related quality of life, construct validity, test-retest reliability

3. Authors

The NIH-CPSI was developed by a multidisciplinary panel of urologists, psychometricians, biostatisticians, and health services researchers under the auspices of the Chronic Prostatitis Collaborative Research Network (CPCRN) supported by the National Institutes of Health (NIH) and the NIDDK.

• Mark S. Litwin, MD, MPH (Lead Investigator): Department of Urology, David Geffen School of Medicine at the University of California, Los Angeles (UCLA), and Department of Health Policy and Management, UCLA Fielding School of Public Health, Los Angeles, California, USA.
• J. Curtis Nickel, MD, FRCSC: Department of Urology, Queen’s University, Kingston, Ontario, Canada.
• Richard B. Alexander, MD: Division of Urology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
• Anthony J. Schaeffer, MD: Department of Urology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.
• Kathleen J. Propert, ScD: Department of Biostatistics and Epidemiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA.
• CPCRN Study Group Investigators: A collaborative consortium of academic medical centers across the United States and Canada dedicated to the clinical characterization and therapeutic evaluation of male pelvic pain disorders.

4. Purpose

The primary clinical and psychometric purpose of the NIH-CPSI is to provide an objective, standardized, and reproducible measurement tool for quantifying the severity, distribution, and functional consequences of symptoms in men diagnosed with chronic prostatitis/chronic pelvic pain syndrome. Prior to the publication of the NIH-CPSI by Litwin and colleagues in 1999, clinical assessment of male pelvic pain relied on ad-hoc questionnaires or instruments adapted from other conditions, such as the American Urological Association Symptom Index (AUA-SI / IPSS). However, the AUA-SI primarily captures lower urinary tract symptoms (LUTS) secondary to benign prostatic hyperplasia and entirely omits pelvic pain, the hallmark and clinically predominant feature of CP/CPPS. Consequently, clinical trials and therapeutic monitoring suffered from marked methodological heterogeneity and an inability to detect meaningful patient-centered outcomes.

Clinically, the NIH-CPSI serves several distinct functions across diagnostic, phenotyping, and evaluative spectra:

• Symptom Quantification and Baseline Profiling: It establishes a baseline metric of symptom severity across the multidimensional domains of pain, micturition, and functional impairment. Clinicians utilize these scores to stratify patients into mild (0–14), moderate (15–29), or severe (30–43) symptom categories, enabling tailored interventional strategies.
• Phenotypic Mapping: In modern multimodal management, such as the UPOINT clinical phenotyping system (Urinary, Psychosocial, Organ-specific, Infection, Neurologic/systemic, Tenderness), the subscales of the NIH-CPSI directly guide therapy. For instance, high scores on the pain subscale prompt neuropathic, musculoskeletal, or trigger-point interventions, while elevations on the urinary subscale indicate a need for alpha-blockers or anticholinergic pharmacotherapy.
• Treatment Monitoring and Clinical Trial Endpoint: The index provides a sensitive, responsive metric for measuring therapeutic efficacy over time. A reduction of 4 to 6 points, or a 25% decrease in the total score, has been established empirically as the minimally clinically important difference (MCID), distinguishing meaningful therapeutic benefit from placebo response in clinical trials testing anti-inflammatory agents, neuromodulators, pelvic floor physical therapy, and cognitive-behavioral interventions.
• Psychological and Functional Impact Tracking: By segregating quality of life impact into an independent subscale, the instrument prevents the conflation of physical symptom presence with affective distress. This allows health psychologists and behavioral medicine specialists to evaluate how psychological therapies (e.g., acceptance and commitment therapy, pain neuroscience education, cognitive reframing) improve functional outcomes even in instances where nociceptive sensations persist.

5. Psychological Construct

The NIH-CPSI measures the multidimensional experience of chronic urological pain as an integrated biopsychosocial phenomenon. Chronic prostatitis/chronic pelvic pain syndrome (Category III prostatitis) is defined by the persistence of pelvic discomfort or pain for at least three of the preceding six months in the absence of documented urinary tract infection or other identifiable urogenital pathology. The instrument operationalizes this clinical syndrome into three interconnected core constructs: Pain or Discomfort, Urinary Symptoms, and Quality of Life Impact.

1. Pain or Discomfort Construct (Items 1–4)

Pain is the defining diagnostic hallmark of CP/CPPS. Psychometrically, the NIH-CPSI conceptualizes pain across three distinct dimensions: anatomical localization, temporal persistence/frequency, and perceived subjective intensity.

• Anatomical Distribution (Items 1a–1d, 2a–2b): The instrument assesses the presence of pain across four primary somatic locations (perineum, testicles/scrotum, penile tip, and suprapubic/lower abdominal region) and during two functional physiological events (dysuria and post-ejaculatory pain). Post-ejaculatory discomfort is widely recognized as a highly specific marker distinguishing CP/CPPS from interstitial cystitis/bladder pain syndrome and pure lower urinary tract obstruction.
• Temporal Frequency (Item 3): Pain chronicity in pelvic pain syndromes often fluctuates dynamically. Item 3 captures this temporal variability on a 6-point frequency continuum ranging from “Never” to “Always.”
• Perceived Intensity (Item 4): A standard 11-point (0–10) numerical rating scale (NRS) captures average subjective pain intensity on symptomatic days over the preceding week. This anchors the physical sensation to an established psychophysical metric of pain severity.

2. Urinary Symptoms Construct (Items 5–6)

Although lower urinary tract symptoms are secondary to pain in diagnostic hierarchy, voiding dysfunction represents a major source of somatic distress in affected men. The NIH-CPSI focuses on two classical lower urinary tract complaints:

• Obstructive / Incomplete Emptying (Item 5): Measures the subjective sensation of post-void residual urine, reflecting functional bladder neck obstruction, detrusor underactivity, or pelvic floor hypertonicity.
• Irritative / Frequency (Item 6): Evaluates urinary urgency and urinary frequency, specifically querying the need to void again in less than two hours. This captures bladder hypersensitivity, detrusor overactivity, and pelvic autonomic arousal. Both items utilize a 6-point quasi-proportional response format adapted from the IPSS.

3. Quality of Life Impact Construct (Items 7–9)

The psychological construct of health-related quality of life (HRQoL) in the NIH-CPSI measures the disruptive encroachment of somatic sensations onto daily psychological, behavioral, and existential functioning.

• Behavioral / Functional Impairment (Item 7): Measures the degree of behavioral avoidance, role inhibition, and disruption of daily functional activities caused by symptoms over the preceding week.
• Cognitive Preoccupation / Rumination (Item 8): Assesses cognitive intrusion and symptom-directed attentional bias, reflecting the psychological process of pain catastrophizing and hypervigilance. Excessive cognitive focus on pelvic sensations correlates strongly with central pain amplification and depressive symptom severity.
• Global Dissatisfaction / Delighted-Terrible Dimension (Item 9): Utilizes a classical 7-point Andrews and Withey “Delighted-Terrible” scale to evaluate the patient’s global psychological adjustment to living with chronic symptoms indefinitely. This item serves as a sensitive barometer of demoralization and existential burden.

6. Theoretical Framework

The NIH-CPSI is grounded in the biopsychosocial model of health and illness articulated by George Engel (1977), integrated with contemporary neurobiological models of chronic pain processing, including the Gate Control Theory (Melzack & Wall, 1965) and the Fear-Avoidance Model of Chronic Pain (Vlaeyen & Linton, 2000).

Biopsychosocial and Neuro-Immune Integration

Historically, chronic prostatitis was viewed strictly through a biomedical lens, presumed to represent persistent, occult bacterial infection of the prostate gland. However, rigorous microbiological investigations by the NIDDK Chronic Prostatitis Collaborative Research Network demonstrated that less than 5% to 10% of symptomatic men harbor viable uropathogens. Consequently, the conceptual paradigm shifted toward recognizing CP/CPPS as a complex neuromuscular, neuro-immune, and psychological disorder characterized by:

1. Initial peripheral tissue insult (e.g., trauma, microtrauma, transient infection, chemical inflammation).
2. Sustained hypertonicity and myofascial spasm of the pelvic floor musculature (levator ani, obturator internus).
3. Neurogenic inflammation mediated by mast cell degranulation, nerve growth factor (NGF), and pro-inflammatory cytokines (IL-1β, IL-6, TNF-α).
4. Central sensitization of the spinal dorsal horn neurons and supraspinal nociceptive processing pathways (spinothalamic tract, thalamus, insular cortex, and anterior cingulate cortex).

By measuring pain distribution, voiding abnormalities, and psychological impact concurrently, the NIH-CPSI operationalizes this complex interplay, recognizing that central neuroplastic remodeling drives symptom persistence even in the absence of ongoing peripheral pathology.

Cognitive-Behavioral and Health Psychology Paradigms

Within health psychology, the NIH-CPSI aligns with the cognitive-behavioral framework of chronic illness adaptation. When patients experience recurring, unpredictable pelvic pain (often exacerbated by ejaculation or urination), catastrophic cognitive appraisals (“My prostate is permanently damaged,” “This pain will ruin my sexual life”) frequently emerge. These cognitions fuel hypervigilance (Item 8) and behavioral withdrawal (Item 7), which in turn precipitate severe functional demoralization (Item 9). The NIH-CPSI construct design deliberately separates these functional-affective components from pure sensory pain intensity, permitting researchers within large consortia such as the Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP Research Network) to delineate how psychological resilience, emotional distress, and somatic amplification interact dynamically over time.

7. Validity

The psychometric validity of the NIH-CPSI has been extensively substantiated through content, construct, convergent, discriminant, and criterion-related empirical investigations involving thousands of patients across multinational cohorts.

Content and Face Validity

Content validity was established through a structured consensus methodology executed by the CPCRN panel. Candidate items were generated through iterative input from expert urologists, clinical psychologists, health service researchers, and patient focus groups. The panel refined over 30 initial candidate questions down to the core 9 questions to ensure that all critical facets of the clinical syndrome (anatomical pain patterns, voiding patterns, functional limitations, and emotional distress) were exhaustively represented while minimizing respondent burden.

Construct and Known-Groups Validity

In the original validation study by Litwin et al. (1999), the NIH-CPSI demonstrated remarkable known-groups construct validity, sharply differentiating between clinically diagnosed CP/CPPS patients, men with benign prostatic hyperplasia (BPH), and healthy, asymptomatic control subjects:

• CP/CPPS Patients vs. Asymptomatic Controls: Mean total scores for men with CP/CPPS were significantly higher (mean ± SD = 20.6 ± 8.8) compared to healthy control participants (mean = 3.1 ± 4.1; p < 0.001). Furthermore, on the pain subscale, CP/CPPS patients scored an average of 11.2 ± 4.6, whereas healthy controls scored 0.4 ± 1.1 (p < 0.001).
• CP/CPPS Patients vs. BPH Cohorts: While men with BPH scored similarly to CP/CPPS patients on the urinary symptoms subscale (BPH mean = 5.2 ± 2.8 vs. CP/CPPS mean = 4.3 ± 2.6), CP/CPPS patients scored markedly higher on the pain subscale (11.2 vs. 1.8, p < 0.001), corroborating that the pain construct specifically distinguishes CP/CPPS from other urological disorders.

Convergent and Discriminant Validity

Convergent validity has been established by evaluating correlations between NIH-CPSI subscales and established legacy instruments:

• The Urinary Symptoms Subscale correlates strongly with the International Prostate Symptom Score (IPSS) (Pearson’s r = 0.69 to 0.77, p < 0.001), indicating excellent convergent measurement of voiding dysfunction.
• The Quality of Life Subscale correlates moderately to strongly with the Physical Component Summary (PCS) of the SF-36 (r = -0.52 to -0.64) and the Mental Component Summary (MCS) (r = -0.41 to -0.53), demonstrating that higher pelvic symptom impact corresponds to lower general health-related quality of life.
• Discriminant validity is evidenced by weak correlations between the Pain Subscale and unrelated physiological parameters (such as prostate volume measured via transrectal ultrasound, serum prostate-specific antigen [PSA] levels, or urinary flow rates; r < 0.15, non-significant).

Responsiveness and Predictive Validity

The NIH-CPSI exhibits superior longitudinal responsiveness to clinical change. In randomized clinical trials evaluating pharmacotherapies (such as fluoroquinolones, alpha-adrenergic antagonists, and nonsteroidal anti-inflammatory drugs) and behavioral interventions, longitudinal changes in the NIH-CPSI tracked clinical global impressions of improvement. Turner et al. (2004) and Propert et al. (2006) confirmed that a reduction of 4 to 6 points on the total index represents a clinically meaningful threshold (minimally clinically important difference), with receiver operating characteristic (ROC) curves yielding an area under the curve (AUC) of 0.83 to 0.87 for identifying treatment responders.

8. Reliability

The reliability of the NIH-CPSI has been thoroughly documented in multiple clinical and population-based investigations, examining internal consistency, test-retest reproducibility, and measurement error precision.

Internal Consistency Reliability

Internal consistency evaluates the degree to which items within a subscale measure the same underlying construct. Across international psychometric studies, Cronbach’s alpha (α) coefficients consistently satisfy and exceed established psychometric thresholds (α ≥ 0.70 for research, α ≥ 0.80 for clinical decision-making):

• Total Score: α = 0.86 to 0.91 across English, Italian, German, Spanish, Japanese, and Chinese adaptations.
• Pain Subscale (Items 1–4): α = 0.80 to 0.89, indicating cohesive measurement of pain distribution, frequency, and severity.
• Urinary Subscale (Items 5–6): α = 0.72 to 0.81. Because this subscale contains only two items, a Cronbach’s alpha exceeding 0.70 reflects strong inter-item correlation (typical inter-item correlation r = 0.58 to 0.68).
• Quality of Life Subscale (Items 7–9): α = 0.82 to 0.88, demonstrating substantial internal homogeneity regarding the functional, cognitive, and global burden of symptoms.

Test-Retest Reliability

Test-retest stability was initially evaluated in clinically stable patients over a 2-week observation window prior to treatment initiation. Intraclass correlation coefficients (ICC) and Pearson correlation coefficients consistently demonstrate excellent temporal reproducibility:

• Total NIH-CPSI Score: ICC = 0.84 to 0.93 (original Litwin et al. cohort: r = 0.87, p < 0.001).
• Pain Subscale: ICC = 0.80 to 0.91.
• Urinary Subscale: ICC = 0.76 to 0.85.
• Quality of Life Subscale: ICC = 0.81 to 0.89.

Measurement Precision and Standard Error

The standard error of measurement (SEM) for the total score is approximately 2.1 to 2.6 points. Based on this SEM, the minimal detectable change (MDC) at the 95% confidence level ($MDC_{95} = 1.96 \times \sqrt{2} \times SEM$) is approximately 5.8 to 7.2 points. This indicates that a change of 6 points or more represents true clinical alteration beyond statistical measurement artifact.

9. Factor Analysis

The structural dimensionality of the NIH-CPSI has been scrutinized using both exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) across diverse patient populations.

Exploratory Factor Analysis (EFA)

Initial principal components analysis with varimax and oblimin rotations conducted by the CPCRN investigators identified a clear three-factor solution accounting for approximately 62% to 68% of the total shared item variance:

• Factor 1 (Pain/Discomfort): Comprising items 1a–1d, 2a–2b, 3, and 4. Factor loadings for pain location items range between 0.54 and 0.78, while pain frequency (item 3) and pain severity (item 4) exhibit primary loadings > 0.75 onto this latent dimension.
• Factor 2 (Quality of Life / Psychological Impact): Comprising items 7, 8, and 9. These items load heavily onto Factor 2 (loadings ranging from 0.72 to 0.86), confirming that cognitive preoccupation, functional restriction, and global dissatisfaction represent a unified psychosocial reaction construct.
• Factor 3 (Micturition / Voiding Dysfunction): Comprising items 5 and 6, loading cleanly onto a third independent factor with primary loadings > 0.80 and minimal cross-loadings (< 0.20) on the pain or quality of life factors.

Confirmatory Factor Analysis (CFA) and Fit Indices

Subsequent structural equation modeling across international multi-center studies confirmed the three-factor oblique model over alternative unidimensional or two-factor configurations. Model fit indices routinely meet rigorous psychometric adequacy benchmarks:

• Comparative Fit Index (CFI): 0.952 to 0.978 (values > 0.95 indicate superior fit).
• Tucker-Lewis Index (TLI): 0.941 to 0.969.
• Root Mean Square Error of Approximation (RMSEA): 0.048 to 0.059 (values < 0.06 denote close approximate fit), with 90% confidence intervals spanning 0.032 to 0.068.
• Standardized Root Mean Square Residual (SRMR): 0.038 to 0.049 (values < 0.05 reflect minimal residual covariance).

Inter-factor latent correlations indicate that while Pain and Quality of Life are moderately to strongly correlated (φ = 0.58 to 0.68), Urinary symptoms correlate more modestly with Pain (φ = 0.36 to 0.44) and Quality of Life (φ = 0.38 to 0.48). This confirms that micturition symptoms represent a distinct, separable dimension that should not be combined directly with pain intensity into a single sensory score.

10. Instrument / Measurement Tool

The NIH-CPSI is a brief, self-administered questionnaire designed for rapid administration in clinical, outpatient, and research settings.

• Instrument Name: National Institutes of Health-Chronic Prostatitis Symptom Index (NIH-CPSI)
• Target Population: Adult and elderly men experiencing chronic pelvic pain, perineal discomfort, dysuria, or suspected chronic prostatitis/chronic pelvic pain syndrome.
• Administration Mode: Self-administered paper-and-pencil, digital electronic patient portal, or clinician-assisted interview.
• Completion Time: Approximately 3 to 5 minutes.
• Item Count: 9 indexed questions encompassing 13 individual scorable items.
• Authentic Response Scale:
  • Items 1–2: Dichotomous (0 = No, 1 = Yes).
  • Item 3: Frequency scale (0 = Never, 1 = Rarely, 2 = Sometimes, 3 = Often, 4 = Usually, 5 = Always).
  • Item 4: Numerical rating scale (0 = No pain, to 10 = Pain as bad as you can imagine).
  • Items 5–6: Frequency scale (0 = Not at all, 1 = Less than 1 time in 5, 2 = Less than half the time, 3 = About half the time, 4 = More than half the time, 5 = Almost always).
  • Items 7–8: Categorical response scale (0 = None, 1 = Only a little, 2 = Some, 3 = A lot).
  • Item 9: Delighted-Terrible scale (0 = Delighted, 1 = Pleased, 2 = Mostly satisfied, 3 = Mixed [about equally satisfied and dissatisfied], 4 = Mostly dissatisfied, 5 = Unhappy, 6 = Terrible).
• Scoring Structure and Subscales:
  • Pain or Discomfort Subscale (Items 1–4): Calculated by summing affirmative responses for locations (1a–1d; maximum 4), affirmative responses for functional pain (2a–2b; maximum 2), the frequency score (Item 3; 0–5), and the pain intensity score (Item 4; 0–10). Subscale range: 0 to 21.
  • Urinary Symptoms Subscale (Items 5–6): Calculated by summing Item 5 (0–5) and Item 6 (0–5). Subscale range: 0 to 10.
  • Quality of Life Impact Subscale (Items 7–9): Calculated by summing Item 7 (0–3), Item 8 (0–3), and Item 9 (0–6). Subscale range: 0 to 12.
  • Total NIH-CPSI Score: Summation of all three subscales: Pain (0–21) + Urinary (0–10) + Quality of Life (0–12). Total range: 0 to 43.
• Severity Categorization:
  • Mild Symptoms: Total score 0–14
  • Moderate Symptoms: Total score 15–29
  • Severe Symptoms: Total score 30–43
• Clinical Decision Metric: A change of ≥ 4 to 6 points on the total score, or a 25% reduction from baseline, denotes the established Minimally Clinically Important Difference (MCID).

11. Permissions & Fee and Test Year

The NIH-CPSI was developed in 1999 by Mark S. Litwin, MD, MPH, and colleagues within the Chronic Prostatitis Collaborative Research Network, funded directly by research grants from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National Institutes of Health (NIH).

• Fee and Accessibility: As a government-funded instrument developed for the public benefit, the NIH-CPSI is in the public domain. It is freely available for clinical, educational, and academic research purposes without licensing fees or royalty payments.
• Permissions and Usage Guidelines: While formal commercial licensure is not required, investigators and clinicians are required to preserve the wording, structural item sequencing, and response formats to maintain psychometric validity. Commercial entities incorporating the tool into proprietary software or sponsored clinical trials should cite the original source publication appropriately.
• Author Contact and Institutional Affiliation: Correspondence regarding the historical development may be directed to Dr. Mark S. Litwin, Department of Urology, David Geffen School of Medicine at UCLA, Box 951738, Los Angeles, CA 90095-1738, USA.

12. References

Clemens, J. Q., Calhoun, E. A., Litwin, M. S., McNaughton-Collins, M., Kusek, J. W., Crowley, E. M., & Landis, J. R. (2009). Validation of a modified National Institutes of Health Chronic Prostatitis Symptom Index to assess genitourinary pain in both men and women. The Journal of Urology, 182(2), 583–587. https://doi.org/10.1016/j.juro.2009.04.015

Engel, G. L. (1977). The need for a new medical model: A challenge for biomedicine. Science, 196(4286), 129–136. https://doi.org/10.1126/science.847460

Litwin, M. S., McNaughton-Collins, M., Fowler, F. J., Jr., Nickel, J. C., Calhoun, E. A., Pontari, M. A., Alexander, R. B., Farrar, J. T., O’Leary, M. P., & Chronic Prostatitis Collaborative Research Network. (1999). The National Institutes of Health Chronic Prostatitis Symptom Index: Development and validation of a new outcome measure. The Journal of Urology, 162(2), 369–375. https://doi.org/10.1016/S0022-5347(05)68562-X

Melzack, R., & Wall, P. D. (1965). Pain mechanisms: A new theory. Science, 150(3699), 971–979. https://doi.org/10.1126/science.150.3699.971

Nickel, J. C., Downey, J., Hunter, D., & Clark, J. (2001). Prevalence of prostatitis-like symptoms in a population based study using the National Institutes of Health chronic prostatitis symptom index. The Journal of Urology, 165(3), 842–845. https://doi.org/10.1016/S0022-5347(05)66541-X

Propert, K. J., Litwin, M. S., Wang, Y., Alexander, R. B., Calhoun, E. A., Nickel, J. C., O’Leary, M. P., Pontari, M. A., Schaeffer, A. J., & Chronic Prostatitis Collaborative Research Network. (2006). Responsiveness of the National Institutes of Health Chronic Prostatitis Symptom Index (NIH-CPSI). Quality of Life Research, 15(2), 299–305. https://doi.org/10.1007/s11136-005-1317-0

Turner, J. A., Ciol, M. A., Von Korff, M., & Berger, R. (2004). Validity and responsiveness of the National Institutes of Health Chronic Prostatitis Symptom Index in a clinical trial. The Journal of Urology, 171(2), 721–724. https://doi.org/10.1097/01.ju.0.000108655.83648.b4

Vlaeyen, J. W., & Linton, S. J. (2000). Fear-avoidance and its consequences in chronic musculoskeletal pain: A state of the art. Pain, 85(3), 317–332. https://doi.org/10.1016/S0304-3959(99)00242-0

13. Items of the Scale (Questionnaire)