Objectives:
The Secondary Traumatic Stress Inventory (STSI), which is a modified version of the PTSD Symptom List (PCL-5), is designed to assess the symptoms of secondary traumatic stress in professionals working with traumatized individuals. The aim of the study was to determine the psychometric properties of the STSI and establish diagnostic criteria allowing for the assessment of the severity of disorders following secondary traumatic stress.

Methods:
The research was conducted among 900 people representing eight occupational groups exposed to secondary trauma. In total, data from 810 participants was analyzed, the majority of whom (64%) were women. The mean age of the subjects was 43.9 years (SD = 9.60). The STSI was performed in conjunction with several other measurement tools.

Results:
STSI is characterized by a high reliability index (Cronbach’s alpha = 0.94). Four factors were found to correspond to the main criteria of post-traumatic stress disorders, viz. intrusions, avoidance, changes in cognition and emotions, and increased arousal and reactivity. The confirmatory analysis confirmed the validity of adopting the four-factor structure. A cut-off point of 33 was found to be predictive of possible disorders after secondary traumatic stress. The highest risk of disorders was noted among medical personnel, the lowest among therapists and police officers.

Conclusions:
STSI is an accurate and reliable tool for assessing secondary traumatic stress and can be used both in research and clinical practice as a predictor of disorders after secondary traumatic stress.