Part 1 translation content validation and pilot testing
Translation and cross-cultural adaptation process
The GPS was translated and adapted based on the seven-step procedure described by Sousa and Rojjanasrirat (2011) for the cross-cultural translation, adaptation and validation of health-related scales . The translation to Persian/Farsi was completed by two independent translators and reviewed by a committee consisting of a psychiatrist, a psychologist, and a professional English translator to check the clarity of the instructions, format of items and responses, and equivalence of content.
A draft of the translated GPS was then sent to six experts, including two psychiatrists with experience in psychotrauma, one mental health expert, one epidemiologist, and two people with a history of psychotrauma as lay experts. They were asked to rate GPS questions on the relevancy, clarity, and comprehensiveness. The content validation process was conducted in two phases . Inter-rater agreement (IRA) was calculated among the experts for the relevance and clarity of each item on the GPS. The item content validity index (I-CVI) for each question was defined as the proportion of experts and lay experts who chose the item as ‘appropriate/clear’ or ‘quite appropriate/clear’. A cutoff of 80% was considered acceptable for this index. The scale content validity index (S-CVI) was also calculated based on the average method (S-CVI/Ave). The acceptable value for S-CVI/Ave was set at 90%. The same procedure was conducted for relevancy of each GPS item. Comprehensiveness of the GPS was assessed by the proportion of experts who reported that the instrument comprehensiveness was appropriate. The acceptable comprehensiveness was set at 80% [29, 30].
Thirty participants (mean age = 29.13; SD = 9.16; range = 18–49) were recruited via the University and filled out the questionnaire twice in a two-week interval . Intraclass correlation was used to assess test–retest reliability (< 0.40 = poor; 0.41-0.6 = fair; 0.61-0.80 = moderate; > 0.80 = excellent) and Cronbach’s alpha was calculated to assess internal consistency at baseline.
Part 2 epidemiological survey
Participants and procedure
Using a multistage sampling method, a representative sample of 800 adults from Kermanshah, a province in Eastern Iran, were invited to participate in this cross-sectional study from June 2019 to November 2019. All residents of Kermanshah province experienced a 7.3 magnitude earthquake hit Kermanshah on November 12, 2017 and more than 3000 aftershocks after that. The sample was recruited with the help of Kermanshah Medical Sciences University, Kermanshah, Iran. All residents of 8 municipality areas of Kermanshah aged between 18–65 years, constituted the study reference population. These eight areas are stratified based on socioeconomic status. After selecting three areas randomly from stratified municipal areas in Kermanshah city (primary units), 800 households, proportional to the population size of each selected area, were selected as secondary units. Using the Kish method, one eligible family member (aged 18 years or above) in each household was randomly selected . Four trained researchers visited each household and explained the procedures and goals of the research study. After obtaining written informed consent from willing participants, the researchers provided hard copies of the self-report questionnaires. The completed surveys were retrieved after a week in a closed envelop.
Lifetime traumatic events
Data on the presence of lifetime traumatic events were obtained using the questions; “Have you experienced a specific, stressful event during your life, and what is the worst event?”. Responses include 17 options: a) Natural disaster, b) Fire or explosion, c) Transportation accident, d) Serious accident at work, home, or during recreational activity, e) Exposure to toxic substance, f) Physical assault, g) Assault with a weapon, h) Sexual assault, i) Other unwanted or uncomfortable sexual experience, j) Combat or exposure to a war zone (as soldier or civilian), k) Captivity (e.g., being kidnaped, abducted, held hostage, prisoner of war), l) Life-threatening illness or injury, m) Severe human suffering, n) Sudden violent death (e.g., homicide, suicide), o) Sudden accidental death, p) Serious injury, harm, or death you caused to someone else, and q) Any other very stressful event or experience .
Global Psychotrauma Screen (GPS)
The GPS was developed to screen for a wide range of trauma-related psychological problems and risk factors and protective factors. The instrument includes 22 items in a yes/no format. The GPS total score is calculated using all 22 items (range 0–22). The total symptom score is calculated by adding up the 17 symptom items (GPS-Sym; range 0–17 with higher scores indicating higher symptom endorsement).
The instrument subdomain scores are calculated by adding up the items for: PTSD (5 items; range 0–5), Disturbances in Self-Organisation (DSO; 2 items; range 0–2), Anxiety (2 items; range 0–2), Depression (2 items; range 0–2), Sleep problems (1 item; range 0–1), Self-harm behaviour (1 item; range 0–1), Dissociation (2 items; range 0–2), Other physical, emotional or social problems (1 item; range 0–1), and Substance abuse (1 item; range 0–1). A Complex PTSD score is the sum of PTSD and DSO items (7 items; range 0–7). A risk factor score is calculated by adding up the 5 risk and protective items (range 0–5). These include: other stressful events (item 17), Childhood trauma (item 19), History of mental illness (item 20) Social support (item 21), Psychological resilience (item 22). The original validation studies in other languages showed a high reliability and good construct validity of the measure [21,22,23,24,25]. The GPS is currently available in over 30 languages and is freely available on https://www.global-psychotrauma.net/gps.
PTSD Checklist for DSM-5 (PCL-5)
The PCL-5 is one of the most widely used self-report measures of PTSD [34, 35]. This checklist has an adapted and validated version in Persian . The PCL-5 has 20 items and four subscales, corresponding to the symptoms and clusters of the diagnostic criteria of PTSD in the DSM-5: intrusions, avoidance, negative alterations in cognitions and mood, and hyperarousal.
General health questionnaire
The general health questionnaire (GHQ) is a 28-item questionnaire developed by Goldenberg (1972) and translated in Persian by Noorbala, Bagheri, and Mohammad (2009) [36, 37]. This questionnaire includes four subscales: somatic symptoms, anxiety and insomnia, social dysfunction and depression . The authors reported acceptable reliability and validity for this questionnaire [37, 39].
Exploratory and confirmatory factor analysis
The factor structure of the GPS is explored with a tetrachoric exploratory factor analysis (EFA) conducted on a randomly selected subsample of 355 participants (50% of the sample) using the 17 symptom items. The Kaiser-Meyer- Olkin > 0.8 along with Bartlett test for sphericity (p < 0.05) was used for testing the assumptions of EFA. To confirm the hypothesized factor structure, confirmatory factor analysis (CFA) using maximum likelihood estimation was conducted on the remaining 50% of the sample. The following goodness-of-fit indicators were considered as a guide for acceptable model fit: Chi-squared/df < 5, Root Mean Square Error of Approximation (RMSEA) < 0.08, and Comparative Fit Index (CFI), Goodness of Fit Index (GFI), Tucker-Lewis index (TLI) > 0.9, and standardized root mean squared residual (SRMR) < 0.08 [40, 41].
Reliability and validity
We assessed the reliability of the GPS by investigating inter-item and item-total correlations. We assessed the internal consistency of the GPS total symptom score using Cronbach’s alpha. We assessed the convergent validity between the GPS total symptom score, GHQ and PCL-5 with Pearson’s correlation coefficient.
The accuracy of the GPS for identifying individuals presenting probable PTSD diagnosis was assessed using Receiver Operating Characteristic (ROC) analysis. Individuals were divided into two groups using the recommended PCL-5 cut-off score of 33 , to differentiate between those with and without probable PTSD. The Youden index, sensitivity, specificity, and the area under the ROC curve were calculated to estimate the optimal cut-off point for screening accuracy of the GPS total symptom score for probable PTSD.