Participants and procedures
This longitudinal survey study is part of the cohort study You Don’t Stand Alone (37), investigating critical incidents and development of PTSD in a large, public Danish ambulance organisation over a three-year period. We have previously published a cross-sectional study based on the baseline data from the DUSA cohort, which examined individual-level associations between social support utilisation and PTSD symptoms (38). The present study enhances our knowledge on support utilisation in ambulance workers by linking longitudinal organisational data of workload with five waves of longitudinal measures of support utilisation to investigate how workload affects help-seeking over time.
The organisation represents 21.5 percent of all 3271 Danish EMS personnel employed in ambulance services (39), including ambulance rescuer students.
All operational EMSpersonnel (N = 703) in the ambulance organisation were invited to the baseline survey. The sample consists of EMS personnel in operational ambulance duty, including emergency service transport personnel, ambulance rescuer students, ambulance rescuer assistants, ambulance rescuers, and paramedics. The respondents are employed at a station in one of the seven areas in the organisation, apart from a minority of workers employed across stations. Managers were not included as operational EMS personnel, as their engagement in operational duty is lower than that of the employees, and as their utilisation of support was expected to differ from that of the employees.
While all employees were invited to participate at baseline, the survey remained open to new respondents at later waves in order to capture employees who had not responded initially or who had joined the organisation after baseline. Employees who responded to the baseline survey were invited to the 3-, 6-, 9-, and 12-month follow-up surveys, as well as new responders were invited to subsequent follow-up surveys. Inclusion required participation in a minimum of two survey waves.
A total of 462 employees participated at baseline. Of these, 11 were registered as managers and were excluded from the study, yielding a baseline sample of 451 respondents. The analytic sample included 341 participants who provided repeated responses on the outcome measure. This group consisted of 334 individuals enrolled at baseline and 7 who joined the study after baseline but met the same inclusion criteria. At the time of the 12-month follow-up, 642 were employed in operational duty in the organisation, yielding a response rate of 53.2%. Study data were collected and managed using REDCap electronic data capture tools (40, 41) hosted at Region of Southern Denmark.
(Insert Fig. 1)
(Figure titel) Fig. 1: Overview of data collection
Ethics
Participants were informed of the purpose and nature of the survey through an online information sheet, and participation was based on written consent. The project complies with GDPR requirements (the Danish Data Protection Authority, # 20/47381). The study was presented to the Scientific Ethics Committee, which received the formal response that, according to Danish law, the study was not subject to approval by the committee (# 20222000-78).
Measurements
Outcome variable: Social support utilisation
Social support utilisation was the main outcome measured with a modified version of the General Help Seeking Questionnaire (42) targeted towards the context of ambulance work. For this study, we focused on the formalised support types provided by the workplace (formal collegial support by a colleague trained in providing support, formal support by a manager trained in providing support, crisis psychologist through work, debriefing/defusing). Debriefing and defusing is initialised automatically in the ambulance organisation when pre-defined categories of critical incidents are encountered. The management informed that it was customary for all invited workers to participate. The utilisation of debriefing and defusing thus differed from the other formal support types and did not reflect help seeking behaviour in the same sense. We therefore excluded measure of debriefing and defusing from our analyses. Social support utilisation was measured quarterly as depicted in Fig. 1. Answers were given as yes/no for each type of support.
Explanatory variables
Measure of exposure: Workload
Workload was the main explanatory variable of our analyses. The measure of workload was constructed as an index based on organisational data of all emergency responses from three months before the baseline survey and up to the date of the 12-month follow-up survey. The data reflected every single emergency response at the level of station. Data was categorised by date and time. Emergency response data was also coded in relation to response type: acute car, acute medical car, day shift ambulance, 24-hour shift ambulance, effective ambulance, and medical transportation. In Denmark, emergency responses are categorised into A-, B-, or C-responses, indicating the urgency and fatality of the incident, the ambulance is called out to. Because our hypothesis was focused on the overall workload, we chose to include all responses into a sum score for each time point, divided by the number of days for each time period as well as divided by number of EMS workers at the station. This operationalisation reflects an index approximating the workload associated with being employed at the particular station, ranging from 0.10 to 0.38 at the baseline level.
Adjustment variables
Based on extant research, we included several adjustment variables to assess the robustness of the associations between workload and support utilisation. We included age at baseline (measured as whole years) and gender (measured as male, female, or other gender orientation), because both age and gender have been shown to predict support utilisation (43, 44). Post-traumatic stress symptoms (PTSS) and perceived social capital were also included in the analyses. PTSS was included because it have been proposed to affect individual social behaviour patterns including utilisation of support both among EMS personnel and trauma-exposed individuals in general (45, 46). PTSS was measured using the validated Danish version of the International Trauma Questionnaire (ITQ), 6-item version, rated on a five-point Likert scale from “Not at all” (0) to “Extremely” (4) (47, 48). The scale measures PTSS during the past month with two items for each of the three symptom clusters of PTSD: re-experiencing, avoidance, and hypervigilance (47). The scale has shown both good construct validity (49) and criterion validity in different trauma populations (50). Compared to the DSM-5, it has been found to produce statistically significantly lower diagnostic rates (51), which is considered relevant to reduce the risk of over-reporting in a non-clinical population. ITQ has been recommended specifically for assessing PTSS among EMS personnel due to the construct and phrasing of symptoms that resonates with the population’s work exposure (52). The overall symptom level of PTSS was assessed by summing the six items into a sum scale from 0–24, and thus coded as a continuous variable. PTSS was measured as a time variant variable at all five survey waves. The scale showed acceptable to good internal consistency with Cronbach’s Alpha ranging from 0.76 to 0.83 across time points.
Social capital was included in the analyses because the phenomenon can be expected to affect the accessibility of social support sources at work by facilitating co-operation and relational support (53). Individual differences in perceived social capital could thus affect the inclination to rely on help from one’s workplace when distressed. Social capital was measured with the Copenhagen Questionnaire of Workplace Social Capital (54). The full scale measures the experience of respect, justice and the ability to collaborate across different subdimensions of the organisation, i.e. leadership and workers (three items) and groups of workers (four items). As EMS personnel usually work closely in pairs, we added a subscale focusing on the social capital of this partnership. This was done by adapting the wording from the co-worker social capital scale to target the partnership (four items). For all three subscales, the items were answered on a Likert scale from 0 = “never” to 4 = “always”. The scales were summed into a continuous variable, according to manual, as a measure of the overall social capital of the daily workplace. The overall social capital scale was measured at baseline and treated as a time-constant variable. Cronbach’s alpha of the scale showed good internal consistency (α = .88).
Statistical methods
Preliminary analyses and assumption checks
Missing analyses were performed with Little’s MCAR test. Visual inspection of QQ-plots and residual plots was used to assess assumptions of normality and homoscedasticity in the linear models applied for further analyses. Kolmogorov-Smirnov test was used to test distribution of samples. Residual diagnostics, including influential cases of outliers and uniformity of residuals, was conducted using the DHARMa (55) and the Performance package (56). Risk of multicollinearity was assessed by calculation of variance inflation factor in multivariable regression.
Latent class analysis was conducted on three binary indicators of formal support utilisation at baseline (peer support, leadership support, and psychological crisis support). The purpose was to explore whether the indicators formed distinct latent classes of utilisation, thereby identifying natural patterns in the data, or whether they could be treated as a single outcome in subsequent analyses. Models with one to six classes were estimated.
Preliminary analyses of the predictor variable examined the number of emergency responses, both overall and within different categories (A-, B-, and C) at each time point. This was done to investigate potential variations in emergency response data across stations and over time, as well as the data's suitability for primary analyses.
Estimation of whether participation was influenced by workload the year before baseline was performed with simple linear regression. This was done using linear regression with workload as the explanatory variable of the participation percentage at each station.
We assessed attrition on the outcome variable (formal social support utilisation) by testing whether key baseline characteristics predicted missingness using univariable logistic regressions. This was defined as having responded to outcome measures at baseline, but not at any of the follow-up surveys. Workload, age, gender, social capital, and PTSS at baseline were entered as predictors of dropout.
Main analyses
Descriptive statistics and percentage analyses were performed to generate frequencies, means, and standard deviations. These statistics were calculated for the entire sample and for subsamples of EMS personnel depending on their status on workload (low/high). To compare differences between stations experiencing higher versus lower levels of workload, the workload variable was dichotomised using a median split (median = 0.19) for each of the measurement periods. Stations with values above the median were coded as 1 (high workload), and those below or equal to the median as 0 (low workload), with the latter serving as the reference group. This approach allowed station-level workload status to vary over time, reflecting changes in response activity, while maintaining a fixed threshold for classification based on the overall distribution of workload across the study period. This ensured consistent interpretation of what constituted "high pressure", while capturing temporal variation in exposure.
Main analyses were performed with generalised linear mixed models with a logit link function and binomial distribution, estimated via Laplace approximation, using the lme4 package (57). This approach allows for modelling of a binary outcome while accounting for random effects, capturing the hierarchical structure of the data, based on maximum likelihood estimation. Support utilisation at each time point was entered as the binary outcome. Workload for each quarterly period leading up to each survey wave was set as explanatory variable to assess the longitudinal associations between periods of workload and probability of using formal support at work. We did not include lagged effects (e.g. workload predicting support utilisation at later survey waves), as this was beyond the scope of the present study. A random effect term with the respondent-ID as subject was included to allow different intercepts for each respondent (58).
The analysis was conducted in two steps. At step one, only workload was entered as explanatory variable. At step two, the model was adjusted for effects of age, gender, and workplace social capital at baseline as time-constant variables, as well as PTSS as a time variant adjustment factor. Time was also entered at step two to assess the effect of time. Apart from the latent class analyses, which were performed using M-plus (version 8.11), all analyses were performed in R-studio (version 4.4.2). ChatGPT-5 was used in order to assist with initial coding of data.