As the national comprehensive fire and rescue team, Chinese firefighters have been repeatedly exposed to multiple trauma events during their careers, and they are a group with high occupational trauma exposure. In the Diagnostic and Statistical Manual of Mental Disorders-Fifth Edition (DSM-5), the symptom criteria of post-traumatic stress disorder (PTSD) had been revised by the work group based on theoretical and empirical evidence. The purpose of the current study was to evaluate the applicability of the new diagnostic criteria in Chinese firefighters, a group with high occupational trauma exposure.In order to achieve the research goal, 685 Chinese firefighters who experienced occupational trauma were selected in this study to explore symptom characteristics of PTSD in firefighters. On the one hand, the possible prevalence of PTSD was measured by PTSD Diagnostic Scale for DSM-5 and calculated through the diagnostic criteria. On the other hand, the difficulty and discrimination of each symptom item were calculated by using the item response theory (IRT). Then, confirmatory factor analysis (CFA) was implemented on the sample data. And the best-fitting model was determined by comparing the fit indices of five competing models (the classical four factor model, DSM-5 dysphoric arousal model, the anhedonia model, the externalizing behaviour model and the seven-factor hybrid model). This study also conducted a longitudinal study on the same sample, and further discussed the measurement invariance of the best-fitting model across time by using a CFA invariance testing approach.It was found that the prevalence rate of possible PTSD among firefighters was 2.2%. IRT analysis and item characteristic curve (ICC) for symptoms showed that the Nightmares was the most difficult item, cued distress was the highest level of discrimination in the B symptom cluster. Avoidance of thoughts and avoidance of reminders had a higher level of overlap in the ICCs, indicating that these two items had the same difficulty and discrimination in the C symptom cluster. Feelings of detachment from others was the most difficult item in the D symptom cluster; Diminished interest in activities had the highest level of discrimination in the D symptom cluster. Exaggerated startle response was the most difficult item in the E symptom cluster; Difficulty concentrating had the highest level of discrimination in the E symptom cluster. The results showed that the seven-factor hybrid model in the sample of firefighters was the best-fitting model based on the DSM-5 and the measure invariance had been established of the hybrid model.In conclusion, the results of this study support the applicability of the DSM-5 diagnostic criteria. The hybrid model may truly reflect the PTSD symptom structure of firefighters based on DSM-5, and show the measure invariance over time. This study provides empirical evidence for enhancing further understanding of the psychopathological characteristics of PTSD, and is also conducive to providing targeted psychological services for this population.
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