PTSD Symptom Scale Interview (PSS-I)

Abstract

The PTSD Symptom Scale Interview (PSS-I) is a structured clinical interview designed to assess the presence and severity of symptoms associated with Post-traumatic Stress Disorder (PTSD). Developed by Foa, Riggs, Dancu, and Rothbaum in 1993, the PSS-I is a widely recognized psychometric tool used in both research and clinical settings. It corresponds directly to the diagnostic criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM), particularly focusing on the three main clusters of symptoms: Re-experiencing, Avoidance, and Increased Arousal. The scale provides both a dimensional measure of symptom severity and categorical data for diagnostic determination.

Keywords

PTSD Symptom Scale Interview, PSS-I, Post-traumatic Stress Disorder, Trauma Assessment, Clinical Interview, Symptom Severity, Foa, DSM Criteria.

Authors

Edna B. Foa, Dean S. Riggs, Claudia V. Dancu, Barbara O. Rothbaum.

Purpose

The primary purpose of the PSS-I is to offer a standardized, reliable, and valid method for diagnosing PTSD and quantifying the severity of its associated symptoms following a traumatic event. As a structured interview, it ensures consistent administration and interpretation across different clinicians, reducing potential bias inherent in unstructured clinical evaluations.

The scale serves dual functions: first, as a diagnostic instrument to determine if an individual meets the categorical criteria for PTSD based on the number of required symptoms in each cluster; and second, as a continuous measure to track symptom changes over time, making it invaluable for assessing treatment efficacy in clinical trials.

Construct

The PSS-I measures the psychological construct of Post-traumatic Stress Disorder as defined by the criteria established in the DSM (initially DSM-III-R, later adapted for DSM-IV and subsequent versions). It specifically assesses 17 core symptoms, divided into three distinct clusters.

• Re-experiencing: Intrusive thoughts, nightmares, flashbacks, and psychological or physiological distress upon exposure to reminders of the trauma.
• Avoidance/Numbing: Efforts to avoid thoughts, feelings, or external reminders related to the trauma, along with emotional numbing and restricted participation in life activities.
• Increased Arousal: Persistent symptoms of hypervigilance, exaggerated startle response, irritability, difficulty concentrating, and sleep disturbance.

Validity

The PSS-I has demonstrated strong validity across numerous studies. Concurrent validity is high, particularly when compared to the gold standard diagnostic measure for PTSD, the Clinician-Administered PTSD Scale (CAPS). Research by Foa and Tolin (2000) confirmed that the PSS-I yields comparable diagnostic rates and severity scores to the CAPS, establishing its utility as an efficient yet thorough diagnostic tool.

Furthermore, discriminant validity has been supported, showing that the PSS-I effectively differentiates PTSD symptomatology from symptoms associated with other common comorbid conditions, such as major depressive disorder or generalized anxiety disorder, although some overlap remains, necessitating comprehensive clinical evaluation.

Reliability

The reliability of the PSS-I is well-established, contributing to its clinical utility. The source content explicitly notes strong Inter-rater reliability for the categorical diagnosis of PTSD, with a Kappa coefficient (k) reported at 0.91. This high value indicates excellent agreement between different clinicians administering and scoring the interview.

Additionally, studies have consistently reported high internal consistency for the overall scale score, typically yielding Cronbach’s alpha values in the 0.80s to 0.90s, suggesting that the items reliably measure the underlying PTSD construct. Test-retest reliability has also been deemed acceptable, particularly over short intervals, demonstrating stability of symptom measurement.

Factor Analysis

Early Factor analysis of the PSS-I data generally supported the three-factor structure (Re-experiencing, Avoidance/Numbing, and Arousal) corresponding to the DSM-IV model. This structure confirms that the symptom clusters are empirically distinct yet related components of the overall PTSD syndrome.

While later versions of the DSM (e.g., DSM-5) introduced a four-factor structure, the original PSS-I remains primarily validated for the three-factor model it was designed for, confirming its dimensional stability based on the 17 items.

Instrument

Test Type: Structured Clinical Interview.

Format: 17 items rated on a 4-point frequency/severity scale (0 to 3).

Language Available: English (translations are often available in research settings).

Population Group: Clinical and research populations exposed to traumatic events.

Age Group: Adolescents and Adults (typically 18+ for the standard version).

Population Details: Used across diverse groups, including military veterans, survivors of sexual assault, disaster victims, and individuals undergoing trauma-focused therapies.

Test Methodology: Clinician-administered interview requiring trained personnel. The interviewer probes the respondent regarding the frequency and intensity of each symptom over the past week, referencing a specific index trauma. The scoring system is: 0= Not at all; 1= Once per week or less/a little; 2= 2 to 4 times per week/somewhat; 3= 5 or more times per week/very much.

Keywords

Structured Interview, Trauma, Post-traumatic Stress, Foa, Riggs, Psychometrics, Assessment Scale, Clinical Diagnosis.

Authors

Author ORCID Identifier:

Affiliation Email addresses: [email protected]

Correspondence Address: Center for the Treatment and Study of Anxiety, University of Pennsylvania.

Permissions & Fee and Test Year

The PSS-I was originally developed and published in 1993 (Foa, Riggs, Dancu & Rothbaum). Information regarding current permissions and licensing fees should be sought directly from the primary author, Edna B. Foa, or the associated research institution, as usage terms may vary depending on whether the instrument is used for clinical practice or large-scale research.

Reference’s

• Alvarez-Conrad, Jennifer, Foa, Edna B.; & Zoellner, Lori, A. (2001). Linguistic Predictors of Trauma Pathology and Physical Health.
• Foa, Edna B. & Tolin, David F. (2000). Comparison of the PTSD Symptom Scale-Interview Version and the Clinician-Administered PTSD Scale.
• Hobfoll, Stevan E.; Johnson, Robert J.; & Vranceanu, Ana-Maria. (2007). Child Multi-Type Maltreatment and Associated Depression and PTSD symptoms: The Role of Social Support and Stress.

Items of the PTSD Symptom Scale Interview (PSS-I)

RE-EXPERIENCING (need one): [probe, then quantify]

1. Have you had recurrent or intrusive distressing thoughts or recollections about the trauma?
2. Have you been having recurrent bad dreams or nightmares about the trauma?
3. Have you had the experience of suddenly reliving the trauma, flashbacks of it, acting or feeling as if it were re-occurring?
4. Have you been intensely EMOTIONALLY upset when reminded of the trauma (includes anniversary reactions)?
5. Have you been having intense PHYSICAL reactions (e.g., sweaty, heart palpitations) when reminded of the trauma?

AVOIDANCE (Need three): [probe, then qualify]

6. Have you persistently been making efforts to avoid thoughts or feelings associated with the trauma?
7. Have you persistently been making efforts to avoid activities, situations, or places that remind you of the trauma?
8. Are there any important aspects about the trauma that you still cannot recall?
9. Have you markedly lost interest in free time activities since the trauma?
10. Have you felt detached or cut off from others around you since the trauma?
11. Have you felt that your ability to experience the whole range of emotions is impaired (e.g., unable to have loving feelings)?
12. Have you felt that any future plans or hopes have changed because of the assault (e.g., no career, marriage, children, or long life)?

INCREASED AROUSAL (need two): [probe then quantify]

13. Have you had persistent difficulty falling or staying asleep?
14. Have you been continuously irritable or have outbursts of anger?
15. Have you had persistent difficulty concentrating?
16. Are you overly alert (e.g., check to see who is around you, etc.) since the trauma?
17. Have you been jumpier, more easily startled, since the trauma?

Scoring Key: 0= Not at all, 1= Once per week or less/a little, 2= 2 to 4 times per week/somewhat, 3= 5 or more times per week/very much