Mobile Insight in Risk, Resilience and Online Referral (MIRROR): Evaluating the usage and psychometric properties of an online self-help test after potentially traumatic events

Background: Most people who experience a potentially traumatic event (PTE) recover on their own. A small group of individuals develops psychological complaints but is often not detected in time or guidance to care is suboptimal. To identify these individuals and encourage them to seek help, a web-based self-help test called MIRROR– Mobile Insight in Risk, Resilience and Online Referral – was developed. MIRROR takes an innovative approach since it integrates both negative and positive outcomes of PTEs and time since the event, and provides direct feedback to the user. Objective: To assess MIRROR’s usage, examine its psychometric properties (factor structure, internal consistency, convergent and divergent validity) and evaluate how well it classifies respondents into different outcome categories compared to reference measures. Methods: MIRROR was embedded in the website of Victim Support Netherlands so visitors could use it. We compared MIRROR’s outcomes to reference measures of PTSD symptoms (PTSD Checklist for DSM-5), depression, anxiety, stress (Depression Anxiety Stress Scale 21), psychological resilience (Resilience Evaluation Scale) and positive mental health (Mental Health Continuum Short Form). Results: showed good internal consistency, convergent and divergent validity. Exploratory and confirmatory factor analyses yielded a two-factor model with good model fit, conceptual meaning and parsimony. MIRROR correctly classified respondents into different outcome categories, compared to the reference measures. Conclusions: MIRROR is a valid and reliable self-help test to identify negative (PTSD complaints) and positive outcomes (psychosocial functioning and resilience) of PTEs. MIRROR is an easily accessible online tool that can help victims of PTEs to timely identify psychological complaints and to find appropriate support, a tool that might be highly needed in times of the Coronavirus pandemic. (JMIR Preprints 30/04/2020:19716) DOI: https://doi.org/10.2196/preprints.19716


Introduction
Most people will experience at least one potentially traumatic event (PTE) in their lives [1][2][3][4][5]. The impact of PTEs is not the same for every individual. Research shows that most individuals are able to maintain a healthy level of functioning or resilience after experiencing a PTE and psychological complaints usually diminish over time without professional support [1,[6][7][8][9][10]. However, a small but significant group of individuals develops psychological complaints -such as post-traumatic stress disorder (PTSD) -that require care [2].
Experiencing psychological complaints a few days to weeks after a PTE is often considered normal [11][12][13]. The National Institute for Health and Care Excellence (NICE) advises to consider active monitoring -also known as watchful waiting -following a PTE, i.e., regular monitoring of people with some PTSD symptoms within one month of the event [14]. The TENTS guideline for post-disaster psychosocial care advises against formal screening of everyone affected by a PTE, but stresses the importance of identifying individuals in need of support. Once a PTSD has been diagnosed, early treatment is advised [14][15][16][17][18]. Taking these advices together, it could be concluded that support for victims of PTEs is necessary, preferably early and easily accessible.
Unfortunately, the small but significant group that develops persisting psychological complaints is often not detected in time or guidance to care is suboptimal [19,20]. Guidance to care can be hindered due to people not recognizing their symptoms or having self-stigma, which prevents them from seeking help [21][22][23][24]. In addition, health care facilities may lack the resources to be able to reach victims of PTEs and identify the ones who need support [23,25]. Also, general practitioners may not recognize PTSD symptoms [26] or other psychological complaints [27].
In order to prevent the development and persistence of trauma-related complaints, timely and accurate identification is needed [23,28]. Short and easy to use screening instruments could enable individuals at risk of developing psychological complaints to self-identify and monitor possible symptoms after PTEs. Moreover, providing online or mobile self-help tests can aid in timely identification of symptoms in victims of PTEs, providing more information regarding normal psychological responses and in encouraging help seeking [29,30].
Multiple studies show that when one chooses to assist victims of PTEs, it is important to support self-reliance and resilience [1,11,14]. Normalizing and validating emotional responses can promote the capacity to deal with these emotions [11]. Also, the extent to which individuals indicate themselves as being resilient is considered to positively influence post-trauma outcomes [31,32].
Several self-report screening instruments are available to predict PTSD, such as the Trauma Screening Questionnaire, Impact of Event Scale-Revised or PTSD checklist for DSM-5 [33,34].
However, most instruments only screen for complaints and do not inquire about protective factorssuch as psychological resilience and psychosocial functioning [33,34]. In addition, most screening instruments do not consider the time period that has passed since the event. Such information is necessary to determine whether or not reported complaints can be appraised as 'normal' given the stressful event just happened or whether referral to care is needed [14]. By not including time in classifying responses, screening can overlook or misappraise the different response trajectories that have been found after PTEs [9].
To incorporate above guideline advices and address the aforementioned concerns in the early support of victims of PTEs, MIRROR -Mobile Insight in Risk, Resilience and Online Referral -was developed. MIRROR is a web-based self-help test with the potential to reach large groups of victims of PTEs who are seeking reassurance on how they are coping. MIRROR takes an innovative approach since it integrates both negative and positive outcomes of PTEs and time since the event. In compliance with NICE, TENTS and DSM-5 guidelines [14, 15,35], MIRROR's algorithm includes as main weight factors: the severity of complaints, time passed since the event, and level of psychosocial functioning. MIRROR provides victims with personal advice and follow-up support options such as a reminder for self-monitoring. Giving personal feedback to users is recommended to augment the use of mobile self-tests after PTEs [36]. Also, arranging active monitoring with followup within one month is advised [14]. Of relevance, no difference has been found between responses on a PTSD self-report administered via a mobile device versus paper administration [37]. MIRROR aims to contribute to the early identification of those who are likely to develop psychological complaints and encourage them to seek help. At the same time, MIRROR aims to support selfreliance by facilitating self-monitoring and self-recovery through follow-up support options.
While it is recognized that mobile applications have the potential to improve timely identification of complaints and delivery of mental health support after PTEs, there is very little research on their validity, reliability, and effectiveness [29,30,38]. Therefore, the aims of this study were to: 1) assess MIRROR's usage, 2) examine MIRROR's psychometric properties (factor structure, internal consistency, convergent and divergent validity) and 3) evaluate how well MIRROR classifies respondents into different outcome categories compared to reference measures.

MIRROR
A multidisciplinary team of professionals in the field of psychotrauma (clinicians, researchers, and policy officers) and victim and crisis support developed MIRROR. The items and algorithm were based on existing protocols -DSM-5 and ICD-10 [35,39] -best practices and recommendations of the Dutch National Multidisciplinary Guideline on Psychosocial Support in Disasters and Crises [40] and international guidelines for PTSD and post-disaster psychosocial care [14,15].
MIRROR consists of two parts. Part one includes items regarding event-related characteristics: type of event -measured with all events of the Dutch version of the Life Events Checklist for the DSM-5 [41], time passed since the event (measured in weeks), and relation to the event (happened to me, learned about it, witnessed it, part of my job). Part two consists of eight items divided in three sections. The first concerns 'PTSD core symptoms' (four items in total; one about intrusion, two about avoidance and one about arousal). The items are developed based on the clusters in the DSM-IV, DSM-5, ICD-10 and ICD-11. Higher scores reflect more PTSD symptoms. The second concerns the item 'how would you rate your present functioning (at work/home)?', based on the widely used Global Assessment of Functioning (GAF) score for which higher scores reflect a higher level of functioning. The third concerns 'resilience' (three items in total; about social support, self-reliance and problem solving), based on the resilience concept as introduced by Van der Meer et al. 2018 [42]. Higher scores reflect more resilience. PTSD and resilience items are answered on a 5-point response scale, ranging from 1 (never) to 5 (all the time). Functioning is rated on a scale from 1 to 10.
MIRROR's algorithm aims to identify PTSD symptoms, psychosocial functioning and resilience; to normalize complaints -i.e. reassuring users that is it normal to experience distress shortly after a PTE; and to stimulate seeking support in users with persisting complaints. See the multimedia appendix for an overview of the algorithm. In the algorithm, MIRROR's PTSD scale and functioning item are classified in three levels: low, moderate and high. Resilience is categorized as either low or high. The categorizations are based on the aforementioned existing protocols and best practices. MIRROR's algorithm differentiates three phases of time passed since the event: 1) less than one week ago, 2) between one and four weeks and 3) more than four weeks or reoccurring.
These were based on the assumption that complaints after PTEs may occur, but generally will diminish over time; as most people recover on their own [6]. Therefore, the occurrence of PTSD core complaints with moderate to low functioning shortly after an adverse event can be seen as normal [11][12][13], but if complaints and moderate to low functioning are present after one month guidance to care is needed [14][15][16][17][18] MIRROR summarizes the outcome of its algorithm to respondents as either green, orange or red. Together with this color outcome respondents receive personal advice. The color outcome is based on the level of complaints, functioning and time passed since the event. MIRROR's resilience scale is not included in the color outcome because based on current research it is unclear precisely how resilience interacts with the development of PTSD complaints and functioning after PTEs.
Nontheless, resilience is integrated in the personal advice to stimulate the use of social support. If respondents score low on resilience they are encouraged to seek support from close ones and individuals who have experienced similar events.
A green outcome indicates little complaints and/or sufficient functioning. Therefore, the accompanying advice states no further action is needed. An orange outcome indicates complaints and moderate functioning in combination with a PTE that happened only recently (i.e. less than one month). The accompanying advice is directed at normalizing complaints -combined with promoting watchful waiting and encouraging to set a reminder to use MIRROR again in two weeks to assess if complaints have diminished. The red outcome indicates significant complaints (i.e. low functioning or complaints with moderate to low functioning for a longer period or due to a reoccurring event) which persisted for more than a month. Therefore, the advice aims to encourage the user to seek consultation with a general practitioner or to contact Victim Support Netherlands. MIRROR provides follow-up support options with its advice, such as the opportunity to get in touch with people who have had similar experiences, reading information about dealing with stress reactions or setting a reminder to use MIRROR again in two weeks.

Participants and procedure
MIRROR was available in the Dutch language on the website of Victim Support Netherlands Data collection took place between February and August 2019. Only original answers were saved in the database. That is, if respondents went back to change their answers once they already received their advice, changes were not saved. We followed data cleaning recommendations by Birnbaum [43] and Wood et al. [44]. Data were discarded when respondents did not complete all survey items. In case of identical answers on all items of the different reference measures, other systematic answering patterns, or obvious unusual missing answers on certain measures, we reviewed individual results thoroughly and discarded the data in case of doubt.

PTSD symptoms
To measure PTSD symptoms, we used the Dutch version of the PTSD Checklist for DSM-5; PCL-5 [45,46]. The PCL-5 consists of 20 items and measures symptoms of intrusion (cluster B, five items), avoidance (cluster C, two items), negative alterations in cognitions and mood (cluster D, seven items) and alterations in arousal and reactivity (cluster E, six items) in the past month. All items are answered on a 5-point scale, ranging from 0 (not at all) to 4 (extremely). The PCL-5 showed good psychometric properties in different languages [47][48][49]. The total score was calculated by adding all item scores. Scale scores per cluster were calculated by adding the scores of the corresponding items.
Higher scores reflect more severe symptoms. Cronbach's alphas in our sample ranged between .77 and .86 for the B, C, D and E clusters.
The DSM-5 rule to determine a provisional PTSD diagnosis was followed. This entails treating each item with a minimum score of 2 as a symptom endorsed and requiring at least one B symptom, one C symptom, two D symptoms, and two E symptoms [45].

Depression, anxiety, and stress
To assess other common psychological complaints after PTEs, we used the Dutch short version of the Depression Anxiety Stress scale (DASS-21) measuring depression (seven items), anxiety (seven items) and stress (seven items) [50,51]. The DASS-21 is a valid and reliable measure [52,53]. Item scores were summed to calculate scale scores and the total score. Higher scores reflect more severe symptoms. In our sample , Cronbach's alphas were .92, .86 and .86 for depression, anxiety and stress scales respectively. A 4-point response scale measures the extent to which each state has been experienced over the past week ranging from 0 (not at all) to 4 (most certainly). To determine cut-off values, DASS-21 scale scores were multiplied by two, in accordance with the scale's manual [51].

Psychological resilience
We used the Resilience Evaluation Scale (RES) to assess psychological resilience [42]. The 9 items are rated on a 5-point scale ranging from 0 (strongly disagree) to 4 (strongly agree). We calculated the total score by adding all items. Higher scores reflect more psychological resilience. The RES is a valid and reliable measure [42]. In this sample, Cronbach's alpha of the total scale was .88.

Positive mental health
We assessed positive mental health with the Dutch version of the Mental Health Continuum Short Form (MHC-SF) [54,55]. The MHC-SF measures emotional wellbeing (3 items), social wellbeing (5 items) and psychological wellbeing (6 items). Items were rated on a 5-point scale ranging from 0 (never) to 5 (every day). The MHC-SF is a valid and reliable instrument [55,56]. We calculated the total score by summing all item scores. Higher scores reflect more positive mental health. In this sample, Cronbach's alpha of the total scale was .93.

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Sample
Since participation in the research survey was optional, this resulted in two samples. The "MIRRORonly sample" consists of respondents who only completed MIRROR. The "validation sample" includes respondents who completed MIRROR and the accompanied survey with reference measures before receiving their advice. The total sample combines these two samples, consisting of all respondents. To examine if the validation sample was representative of 'the MIRROR user', we used independent-samples t-tests in SPSS version 23 [57] to compare the MIRROR-only sample with the validation sample based on their MIRROR scores and event-related characteristics.
We used the total sample to evaluate MIRROR's usage and to examine MIRROR's factor structure and internal consistency, because for these analyses only data from MIRROR were needed.
We used the validation sample to examine MIRROR's convergent and divergent validity and to evaluate how well MIRROR classifies respondents into different outcome categories, because for these analyses data from MIRROR as well as reference measures from the accompanied survey were needed.

MIRROR's factor structure
We used MPlus version 8 [58] to conduct exploratory factor analysis (EFA) using geomin rotation and confirmatory analysis (CFA). EFA assumes that any item may be associated with any factor. CFA specifies expected relationships between the items and their underlying latent factors. Because items of MIRROR's PTSD and resilience section were categorical they were treated as ordinal and therefore the means and variance adjusted weighted least square (WLSMV) estimator was used. An underlying normal distribution was assumed for each ordinal item, where the five response categories were divided by four thresholds which were estimated from the data. MIRROR's functioning item has ten response categories and was treated as continuous. Because MIRROR's factor structure was not tested before, several models with different number of latent factors were examined using EFA. To assess the model with the optimal number of latent factors needed to adequately account for the correlations among item scores, we used Kaiser criterion (i.e. eigenvalues of the latent factors > 1) and model fit statistics. The model with the best balance between model fit, parsimony and conceptual interpretability was selected as the most optimal model. Subsequently, CFA was used to test the optimal model based on EFA. The difference in goodness-of-fit between nested models was evaluated with the 'difftest' option in MPlus for appropriate χ 2 difference testing with the WLSMV estimator [58]. The χ 2 difference test is highly sensitive to sample size such that even trivial differences between two nested models may be significant [59]. Therefore, we also assessed the difference in CFI. A difference in CFI < 0.01 indicates a better fit of the nested model compared to the more complex model [59]. For EFA and CFA, the model fit indices Comparative Fit Index (CFA), Tucker-Lewis Index (TLI), and Root Mean Square Error of Approximation (RMSEA) were used to evaluate model fit. Model fit can be considered good when CFI and TLI are close to .95, and RMSEA < .06 [60]. If RMSEA < .08 model fit can be considered adequate [60].

Internal consistency
We evaluated internal consistency of MIRROR's PTSD and resilience section with inter-item correlations, corrected item-total correlations and Cronbach's alpha in SPSS version 23 [57].
Internal consistency of MIRROR's functioning section could not be evaluated since it is represented by only one item. When most inter-item correlations are in the recommended range of .15 -.50 (moderate magnitude) and Cronbach's alpha for the scale is > .80, internal consistency can be considered as good [61]. Cronbach's alpha is a function of scale length, and therefore is likely to be lower for MIRROR's scales since they consist of 3 or 4 items [61]. Corrected item-total correlations were computed to assess whether item scores regarding PTSD and resilience are associated with overall PTSD and resilience scores.

MIRROR's classification quality
To evaluate how well MIRROR classifies respondents into a red, orange, or green outcome, we tested whether respondents in these three outcome categories differed on related reference measures by using cross-tabs and ANOVA. If the assumption of equal variances was violated, we used the Welch F test and Games-Howell post hoc test. MIRROR's PTSD scale score was calculated by summing the four PTSD items. Higher scores reflect more severe symptoms. MIRROR's resilience scale score was calculated by a summing the three items. Higher scores reflect more resilience.
Provisional PTSD diagnosis based on PCL-5 were used to classify respondents. To examine the distribution on depression, anxiety and stress symptoms, respondents were classified by comparing their scores to a Dutch clinical reference group. Respondents with normal and mild complaints compared to the reference group were classified into one group representing sub-clinical complaints.
Respondents with average, severe and very severe complaints compared to the reference group were classified into another group, representing clinical complaints. Since no reference groups were available with regard to the RES and MHC-SF, the sample was divided into tertiles (i.e. three groups of equal size divided by the 33 rd and 66 th percentile) based on the total scores of the RES and MHC-SF. With regard to the RES, the first tertile (scores ≤ 17) was assumed to represent relatively low psychological resilience, the second tertile (scores between 18 -24) relatively moderate psychological resilience, and the third tertile (scores between ≥ 25) relative high psychological resilience. With regard to the MHC-SF, the first (scores ≤ 23), second (scores between 24 -47), and third tertile (scores ≥ 48) were respectively assumed to representrelatively low, moderate, and high positive mental health.

Sample
MIRROR was completed 1314 times in the study period of six months. 682 (51.9%) respondents started the research survey. We deleted 51 respondents who indicated to have used MIRROR on behalf of a family member, partner, friend or colleague who experienced a PTE. We deleted 37 repeated measurements, completed by respondents who set a reminder. We excluded 95 respondents because they did not complete all research survey items. After thorough investigation of the answering patterns, we deleted 19 respondents because of unusual answering patterns. A total of 1112 respondents (84.6%) respondents were retained in the total sample, of whom 663 respondents (59.6%, validation sample) also completed all questionnaires of the accompanying research survey. Table 1 Table 1. Overall, the validation sample can be considered representative of all MIRROR users in this study period.    Table 3 presents the factor loadings for the two-factor and three-factor solution model of MIRROR as estimated by EFA. EFA yielded a three-factor solution with good model fit based on all fit indices.

MIRROR's factor structure
The Kaiser criterion was met for the first two factors, eigenvalues of the third until eight factor were <1. The three-factor solution separated MIRROR's PTSD items into two factors; one factor with the intrusion item and one factor with the avoidance and arousal/reactivity items. However, item 2 ("have you become jumpy and/or vigilant since the event?") cross-loaded significantly on two factors within the model, with only a small difference between the two factor loadings (λ = 0.030).
This indicates that item 2 did not sufficiently distinguish between both factors. The three-factor solution clustered the functioning item with the resilience items into a third factor. EFA yielded a two factor solution with adequate model fit. The RMSEA and TLI indicated adequate model fit and CFI indicated good model fit (Table 3.). The Kaiser criterion was met for the first two factors, eigenvalues of the third until eight factor were <1. The first factor of the two-factor solution consisted of the PTSD items and the second factor consisted of the functioning and resilience items. No cross-loadings were observed in this model.
Next, we conducted CFA to further compare the two-and three-factor model that resulted from EFA. Table 4 presents the model fit indices based on CFA of both aforementioned models. The model fit indices were similar for both models; the CFI and TLI indicated good model fit, the RMSEA acceptable model fit. As indicated by the significant χ 2 difference test, the two-factor model has worse model fit compared to the three-factor model (χ 2 (2, N= 1112) = 13.63, P=.001). However, the difference in CFI is < 0.01, indicating the two-factor model does not have worse model fit. We selected the two-factor model as the best-fitting model to our data, given the χ 2 difference test is sensitive to sample size, the CFI difference is <.001 and because it is more more parsimonious and better interpretable at a conceptual level compared to the three-factor model. The two-factor model represents a clear distinction between negatively formulated outcomes (PTSD complaints) and positively formulated outcomes (psychosocial functioning and resilience) of PTEs. The positively formulated outcomes combine psychosocial functioning, social support, self-reliance and problem solving. We therefore propose to rename this factor "psychosocial resources".

Internal consistency
Inter

Convergent and divergent validity
Pearson correlations between MIRROR and reference measures are presented in Table 5. MIRROR's PTSD scale showed strongest correlations with PTSD as measured with the PCL-5, followed by a lower but still substantial correlation with psychological complaints as assessed with the DASS-21.
The weakest correlations were observed between PTSD symptom severity as assessed with MIRROR and psychological resilience and positive mental health. MIRROR's resilience scale showed strongest correlation with psychological resilience (RES), followed by a slightly lower correlation with positive mental health, psychological complaints (DASS-21) and PTSD (PCL-5).
MIRROR's functioning item showed strongest correlations with psychological complaints (DASS-

MIRROR's outcome classification
We expected respondents with the red MIRROR outcome to report more PTSD symptoms and depression, anxiety and stress complaints, and lower psychological resilience and positive mental health compared to respondents with the green and orange MIRROR outcome. Table 6. presents the means and standard deviations on the reference measures for each MIRROR outcome category. We conducted several one-way between-groups analysis of variance (ANOVA) to investigate the difference in mean scores on the reference measures between MIRROR outcome categories. As can be seen, negative outcomes were highest for the red MIRROR outcome category and positive outcomes highest for the green outcome category. The ANOVA results are shown in table 7. We found significant differences in PTSD symptoms, depression anxiety and stress, psychological resilience and positive mental health between groups. Post hoc tests revealed that PTSD symptoms, depression, anxiety and stress complaints were significantly different between all groups (P<.001).
Psychological resilience was significantly higher for the green and orange MIRROR outcome category compared to the red category (P<.001). It was also significantly higher for the green category compared to the orange category (P= .010). Positive mental health was significantly higher for the green and orange category compared to the red category (P<.001). There was no significant difference between the green and orange category (P= .069). The assumption of equal variances was violated. Therefore, the Welch F test and Games-Howell post hoc test were used.

Principal Results and Comparison With Prior Work
The purpose of this study was to evaluate the usage and psychometric and classification properties of MIRROR. MIRROR is an innovative web-based self-help test to identify individuals who develop psychological complaints after a potentially traumatic event (PTE), encourage them to seek help and support self-reliance. Our results indicated that MIRROR is a valid and reliable self-help test to identify negative outcomes (PTSD core symptoms) and positive outcomes (psychosocial functioning and resilience). MIRROR is able to correctly classify respondents according to their PTSD complaints and scores on reference measures. During the study period, 87.95% of respondents that started MIRROR completed it.
We found that MIRROR's presupposed model of three factors (PTSD symptoms, psychosocial functioning and resilience) did not fit our data best. Instead, a two-factor solution showed good model fit, conceptual meaning and maximum parsimony. This model separates MIRROR's PTSD items from the functioning and resilience items (social support, self-reliance and problem solving). In retrospect, the grouping of the functioning and resilience items is not entirely surpising. If we assume stress to be the result of an imbalance between perceived external and internal demands and perceived personal and social resources [62], it is likely that this distinction between demands and resources is reflected in the way people cope with PTEs. We propose to call the factor "psychosocial resources". In accordance with this distinction, the two-factor model clearly separates negative (PTSD complaints) and positive (psychosocial resources) outcomes of PTE's. This is in line with the general notion that PTSD and psychosocial resources are separate constructs [63][64][65].

Future Research and Limitations
Although guidelines on screening for PTSD complaints and post-disaster psychosocial care are widely available [7,15,[69][70][71] [25,73] it is generally not recommended to perform formal screening of complaints among all involved people following incidents. At the same time, we know that early recognition and timely referral to help are essential for preventing and treating traumatic stress symptoms. This is supported by evidence of the effectiveness of early psychological interventions for individuals pre-screened with traumatic stress symptoms shortly following trauma, and no benefits in those not pre-screened for these symptoms [16]. Mobile applications such as MIRROR can make a contribution to solving the "screening dilemma" by supporting low key, accessible and easy to use self-assessment and -monitoring. In this view, MIRROR could be implemented as a first step in the support for victims of PTEs, before having to consult professional care [29,36]. Our study has some limitations. The sample is a specifically targeted sample, because it consisted of visitors of the website of Victim Support Netherlands. Considering website visitors were automatically led to MIRROR when searching for information regarding stress reactions following a PTE, a high prevalence of psychological complaints after traumatic exposure in our sample could be expected. It demonstrates that the intentionally targeted sample was reached. The main strength of this study is by comparing MIRROR to broader-used reference measures, it contributes to the highly needed evidence-base of mobile applications with the potential to improve timely identification of psychological complaints [29,30].

Conclusions
Concluding, this study shows that MIRROR is a psychometrically sound, anonymous and easyaccessible self-help test for victims of PTEs. It is able to identify both negative (PTSD symptoms) and positive (psychosocial resources) outcomes of PTEs and to classify respondents in accordance with reference measures. This study will hopefully contribute to enhancing adequate and timely identification of people who suffer from psychological complaints after PTEs.

Data Sharing Statement
The datasets generated and analysed during this study are available from the corresponding author on reasonable request.

Conflict of interest
This study has been conducted by the independent research center ARQ Centre of Expertise for the Impact of Disasters and Crises and ARQ Centre'45. The funders (ARQ National Psychotrauma Centre, Interreg North-West Europe and Victim Support Netherlands) had no influence on the outcomes of this study.

Funding
This study was partially funded by the Interreg North-West Europe Programme whom invested in the eMEN project, an EU-wide platform for e-mental health innovation and implementation formed by private and public partners in North West Europe [74]. This study was also funded by ARQ National Psychotrauma Centre and Victim Support Netherlands.