Preventing PTSD, depression and associated health problems in student paramedics: protocol for PREVENT-PTSD, a randomised controlled trial of supported online cognitive training for resilience versus alternative online training and standard practice

Interoceptive technologies for psychiatric interventions: From diagnosis to clinical applications

Interoception-the perception of internal bodily signals-has emerged as an area of interest due to its implications in emotion and the prevalence of dysfunctional interoceptive processes across psychopathological conditions. Despite the importance of interoception in cognitive neuroscience and psychiatry, its experimental manipulation remains technically challenging. This is due to the invasive nature of existing methods, the limitation of self-report and unimodal measures of interoception, and the absence of standardized approaches across disparate fields. This article integrates diverse research efforts from psychology, physiology, psychiatry, and engineering to address this oversight. Following a general introduction to the neurophysiology of interoception as hierarchical predictive processing, we review the existing paradigms for manipulating interoception (e.g., interoceptive modulation), their underlying mechanisms (e.g., interoceptive conditioning), and clinical applications (e.g., interoceptive exposure). We suggest a classification for interoceptive technologies and discuss their potential for diagnosing and treating mental health disorders. Despite promising results, considerable work is still needed to develop standardized, validated measures of interoceptive function across domains and before these technologies can translate safely and effectively to clinical settings.

Mental health risk factors for shift work disorder in paramedics: A longitudinal study

OBJECTIVES

Depression and anxiety are prominent in paramedics, as is the prevalence of shift work disorder (SWD), a circadian sleep condition comorbid with mental health disorders. However, the role of mental health risk factors for SWD is largely unknown. This study investigated whether mental health levels in recruit paramedics before shift work predicted greater risk of SWD at 6-months into their career and explored whether shift and sleep factors mediated this relationship.

DESIGN

A longitudinal study.

SETTING

Victoria, Australia.

PARTICIPANTS

Recruit paramedics were assessed at baseline (n = 101; ie, pre-shift work) and after 6-months (n = 93) of shift and emergency work.

MEASUREMENTS

At both time points, participants completed self-reported measures of depression (Patient Health Questionnaire-9), anxiety (Generalized Anxiety Disorder Questionnaire-7), and SWD (SWD-Screening Questionnaire). Participants also filled a sleep and work diary for 14-days at each timepoint.

RESULTS

After 6-months of emergency work 21.5% of paramedics had a high SWD risk. Logistic regression models showed baseline depression predicted 1.24-times greater odds for SWD at 6-months. Through Lavaan path analysis we found shift and sleep variables did not mediate the relationship between baseline mental health and SWD risk. Baseline depression was associated with increased sleepiness levels following paramedics' major sleep periods at 6-months. Pre-existing depression levels also predicted greater perceived nightshift workload.

CONCLUSIONS

Our results highlight depression symptoms before emergency work are a risk factor for SWD within 6-months of work. Depression represents a modifiable risk factor amenable to early interventions to reduce paramedics' risk of SWD.

Possible substance use disorders among first responders during the COVID-19 era: a quasi-experimental study of personal and residential vulnerability

Background: During the COVID-19 pandemic possible substance use disorders (SUD) were exacerbated from increased stress and isolation. Experiences of symptomology differ widely by occupations.Objectives: The objectives were to determine if there is a temporal relationship between COVID-19 vulnerability and possible SUDs among first responders, and to examine the association with neighborhood vulnerability.Methods: We conducted an analysis with two distinct cohorts dependent on time of entry: 1) First responders that began counseling prior to COVID-19 and 2) First responders that began counseling after the start of COVID-19. Data were collected at intake from first responders seeking mental health services between 2017 and 2021 at an organization in Dallas/Fort Worth, Texas. The study sample included 195 mostly male (75%) first responders (51% law enforcement officers; 49% emergency medical technicians/firefighters). Bivariate models tested unadjusted relationships between covariates and possible SUD. Adjusted models consisted of a two-level multivariable logistic regression models.Results: Nearly 40% (n = 77) screened positive for a possible SUD. Those beginning counseling after COVID-19 did not have higher odds of SUDs. For every unit increase in neighborhood Severe COVID-19 Health Risk Index at a first responder's residential location there was an increase in the odds of a possible SUD (AOR = 3.14, 95% CI: 1.47, 6.75).Conclusions: Our study highlights the degree to which personal and residential vulnerability to COVID-19 impacted first responders. The increased occupational stress of this population, and an established pattern of maladaptive coping, elucidates the need for preventative and clinical approaches to strengthen the resilience of this population.

The Quality of Life and the Bio-Molecular Profile in Working Environment: A Systematic Review

Working life is characterised by various requirements and degrees of control in meeting these demands. The imbalance of these elements with workers’ resources can result in work-related stress involving the repeated activation of stress response systems. Modifications in the bio-molecular profile may represent a biological signature of individuals’ life experiences and provide evidence on pathways through which such stressors can result in health outcomes. The aim of our systematic review is to characterize the quality of life (QOL) and the bio-molecular profile in the working population, to highlight if the alteration observed might be related to the working conditions. The article query was performed on PubMed, Embase, and Cochrane CENTRAL and results have been presented according to three molecular pathways involved in the stress response: oxidative stress, inflammation, and neuroendocrine activation. The epidemiological sample has been sub-grouped into “clinical” and “non-clinical” populations according to the presence of a diagnosis of psychological disorders. Besides some critical issues, the review highlights the importance of developing a valid array of biological indicators, measurable in non-invasive matrices, sensitive to both derangements from physiological conditions and stress reduction, useful for identifying those groups at higher risk of health outcomes and, eventually, promoting workers’ wellbeing.

Effectiveness of psychosocial interventions in mitigating adverse mental health outcomes among disaster-exposed health care workers: A systematic review

Health care workers worldwide are at an increased risk of a range of adverse mental health outcomes, including posttraumatic stress disorder (PTSD), following the unprecedented demand placed upon them during the COVID-19 pandemic. Psychosocial interventions offered to mitigate these risks should be based on the best available evidence; however, limited information regarding the comparative effectiveness of interventions is available. We undertook a systematic review of psychosocial interventions delivered to health care workers before, during, and after disasters. Eight databases were searched, including the Cochrane Central Register of Controlled Trials, PubMed/MEDLINE, EMBASE, and PsycINFO. Our primary outcomes were changes in symptoms of PTSD, anxiety, depression, and sleep. We calculated effect sizes, where unreported, and reliable change indices to appraise intervention effectiveness. The study was registered with PROSPERO (CRD42020182774). In total, 12,198 papers were screened, 14 of which were included in the present review. Interventions based on evidence-based protocols, including individual and group-based cognitive behavioral therapy (CBT) for PTSD, anxiety, and depression were found to lead to reliable changes in PTSD and anxiety symptoms. Single-session debriefing and psychological first aid workshops showed limited efficacy. There is limited evidence on psychosocial interventions for health care workers faced with disasters, with the strongest evidence base for CBT-based approaches. Future research should include controlled evaluations of interventions and aim to target identified risk factors.

Pre-deployment programmes for building resilience in military and frontline emergency service personnel

BACKGROUND

Military personnel and frontline emergency workers may be exposed to events that have the potential to precipitate negative mental health outcomes such as depression, symptoms of post-traumatic stress and even post-traumatic stress disorder (PTSD). Programmes have been designed to build psychological resilience before staff are deployed into the field. This review presents a synthesis of the literature on these "pre-deployment resilience-building programmes".

OBJECTIVES

The objective of this review was to assess the effectiveness of programmes that seek to build resilience to potentially traumatic events among military and frontline emergency service personnel prior to their deployment. These resilience programmes were compared to other interventions, treatment as usual or no intervention.

SEARCH METHODS

Studies were identified through searches of electronic databases including Ovid MEDLINE, Embase, PsycINFO, Web of Science and Google Scholar. The initial search took place in January 2019, with an updated search completed at the end of September 2020.

SELECTION CRITERIA

Only studies that used a randomised controlled trial (RCT)/cluster-RCT methodology were included. The programmes being evaluated must have sought to build resilience prior to exposure to trauma. Study participants must have been 18 years or older and be military personnel or frontline emergency workers.

DATA COLLECTION AND ANALYSIS

Studies that met the inclusion criteria were assembled. Data extracted included methods, participants' details, intervention details, comparator details, and information on outcomes. The primary outcomes of interest were resilience, symptoms of post-traumatic stress and PTSD. Secondary outcomes of interest included acute stress disorder, depression, social support, coping skills, emotional flexibility, self-efficacy, social functioning, subjective levels of aggression, quality of sleep, quality of life and stress. Assessment of risk of bias was also completed. A total of 28 studies were included in a narrative synthesis of results.

MAIN RESULTS

All 28 included studies compared an experimental resilience building intervention versus a control or no intervention. There was a wide range of therapeutic modalities used, including cognitive behavioural therapy (CBT) informed programmes, biofeedback based programmes, stress-management programmes, mindfulness and relaxation programmes, neuropsychological-based programmes, and psychoeducational-informed programmes. The main outcomes are specified here, secondary outcomes such as depression, social support, coping skills, self-efficacy, subjective levels of aggression and stress are reported in text. No studies reported on the following pre-specified outcomes; acute stress disorder, emotional flexibility, social functioning, quality of sleep and quality of life. Resilience Eight studies reported resilience as an outcome. We narratively synthesised the data from these studies and our findings show that five of these interventions had success in building resilience in their respective samples. Two of the studies that reported significant results utilised a CBT approach to build resilience, while the other three successful programmes were mindfulness-based interventions. Symptoms of post-traumatic stress Our narrative synthesis of results included eight studies. Two of the eight studies produced significant reductions in symptoms of post traumatic stress compared to controls. These interventions used neuropsychological and biofeedback intervention models respectively. PTSD caseness Four studies reported PTSD caseness as an outcome. Our narrative synthesis of results suggests that evidence is mixed as to the effectiveness of these interventions in reducing clinical diagnosis of PTSD. One study of a neuropsychology-orientated Attention Bias Modification Training (AMBT) programme had success in reducing both symptoms of post-traumatic stress and numbers of participants receiving a diagnosis of PTSD. A stress-management programme reported that, when baseline differences in rates of pre-deployment mental health issues were controlled for, participants in the control condition were at 6.9 times the risk of a diagnosis of PTSD when compared to the intervention group. Given the diversity of intervention designs and theoretical orientations used (which included stress-management, neuropsychological and psychoeducational programmes), a definitive statement on the efficacy of pre-deployment programmes at reducing symptoms of post-traumatic stress and PTSD cannot be confidently offered.

AUTHORS' CONCLUSIONS

While a number of evaluations of relevant programmes have been published, the quality of these evaluations limits our ability to determine if resilience-building programmes 'work' in terms of preventing negative outcomes such as depression, symptoms of post-traumatic stress and diagnoses of PTSD. Based on our findings we recommend that future research should: a) report pre-/post-means and standard deviation scores for scales used within respective studies, b) take the form of large, RCTs with protocols published in advance, and c) seek to measure defined psychological facets such as resilience, PTSD and stress, and measure these concepts using established psychometric tools. This will provide more certainty in future assessments of the evidence base. From a clinical implications point of view, overall there is mixed evidence that the interventions included in this review are effective at safe guarding military personnel or frontline emergency workers from experiencing negative mental health outcomes, including PTSD, following exposure to potentially traumatic events. Based on this, practitioners seeking to build resilience in their personnel need to be aware of the limitations of the evidence base. Practitioners should have modest expectations in relation to the efficacy of resilience-building programmes as a prophylactic approach to employment-related critical incident traumas.

Mechanisms of Change in Trauma-Focused Treatment for PTSD: The Role of Rumination

OBJECTIVE

Cognitive behavioral therapy (CBT) has been well established in the treatment of posttraumatic stress disorder (PTSD). In recent years, researchers have begun to investigate its underlying mechanisms of change. Dysfunctional cognitive content, i.e. excessively negative appraisals of the trauma or its consequences, has been shown to predict changes in PTSD symptoms over the course of treatment. However, the role of change in cognitive processes, such as trauma-related rumination, needs to be addressed. The present study investigates whether changes in rumination intensity precede and predict changes in symptom severity. We also explored the extent to which symptom severity predicts rumination.

METHOD

As part of a naturalistic effectiveness study evaluating CBT for PTSD in routine clinical care, eighty-eight patients with PTSD completed weekly measures of rumination and symptom severity. Lagged associations between rumination and symptoms in the following week were examined using linear mixed models.

RESULTS

Over the course of therapy, both ruminative thinking and PTSD symptoms decreased. Rumination was a significant predictor of PTSD symptoms in the following week, although this effect was at least partly explained by the time factor (e.g., natural recovery or inseparable treatment effects). Symptom severity predicted ruminative thinking in the following week even with time as an additional predictor.

CONCLUSIONS

The present study provides preliminary evidence that rumination in PTSD is reduced by CBT for PTSD but does not give conclusive evidence that rumination is a mechanism of change in trauma-focused treatment for PTSD.

Reply to Van Overmeire, R. Comment on "Tyson, G.; Wild, J. Post-Traumatic Stress Disorder Symptoms among Journalists Repeatedly Covering COVID-19 News. Int. J. Environ. Res. Public Health 2021, 18, 8536"

During the COVID-19 pandemic, journalists reporting on the crisis in the UK were classed as keyworkers [...].

Post-Traumatic Stress Disorder Symptoms among Journalists Repeatedly Covering COVID-19 News

The coronavirus pandemic has resulted in many journalists repeatedly covering stories related to human suffering. This study investigates whether these journalists experienced higher rates of psychological distress, post-traumatic stress disorder (PTSD) and depressive symptoms than those who have been working during the pandemic yet covering stories other than COVID-19 and aims to identify what factors may protect journalists from developing trauma-related symptoms. We assessed journalists (n = 120) working during the COVID-19 pandemic using self-report measures. Journalists repeatedly covering COVID-19 stories had significantly higher psychological distress (η² = 0.04) and PTSD symptoms (η² = 0.08), but not depression, compared to journalists who did not report on COVID-19. Rumination and numbing in response to unwanted memories predicted PTSD symptoms (R² = 0.53) and may be risk factors for PTSD in this population. Unhelpful resilience appraisals distinguished journalists who reported on COVID-19 and who developed distressing re-experiencing symptoms from those who similarly reported on distressing material and who did not develop symptoms. Targeting resilience appraisals may be helpful in reducing re-experiencing symptoms after trauma exposure.

Mental health, well-being and support interventions for UK ambulance services staff: an evidence map, 2000 to 2020

Background:

Prior to COVID-19 there had been a renewed policy focus in the National Health Service on the health and well-being of the healthcare workforce, with the ambulance sector identified as a priority area. This focus is more important than ever as the sector deals with the acute and longer-term consequences of a pandemic.

Aim:

To systematically identify, summarise and map the evidence regarding mental health, well-being and support interventions for United Kingdom ambulance services staff and to identify evidence gaps.

Method:

Evidence mapping methodology of published and grey original research published in English from 1 January 2000 to 23 May 2020 describing the health risk, mental health and/or well-being of UK ambulance services staff including retired staff, volunteers and students. MEDLINE, EMBASE, PsychINFO, CINAHL and AMED databases, plus EThOS, Zetoc, OpenGrey and Google, were searched, alongside hand-searching of grey literature and bibliographies. Information was extracted on study aims, sample, design and methodology, funding source, country and key findings. Included studies were categorised into seven a priori theme areas.

Results:

Of 1862 identified articles, 45 peer-reviewed studies are included as well as 24 grey literature documents. Peer-reviewed research was largely observational and focused on prevalence studies, post-traumatic stress disorder or organisational and individual social factors related to health and well-being. Most grey literature reported the development and testing of interventions. Across all study types, underpinning theory was often not cited.

Conclusion:

To date, intervention research has largely been funded by charities and published in the grey literature. Few studies were identified on self-harm, bullying, sleep and fatigue or alcohol and substance use. Theoretically informed intervention development and testing, including adaptation of innovations from other countries and 24-hour workforces, is needed. This evidence map provides important context for planning of staff well-being provision and research as the sector responds to and recovers from the pandemic.

PROSPERO registration number:

CRD42018104659.

Rumination in posttraumatic stress disorder: A systematic review

Initial models and empirical investigations of rumination in the clinical literature were predominantly in the domain of depression. However, rumination is now well-established as a transdiagnostic cognitive process, including in the context of posttraumatic stress. To clarify the current understanding of rumination in posttraumatic stress, we conducted a systematic review of the empirical literature on rumination in posttraumatic stress disorder (PTSD). Six sub-groups of studies on this topic were identified; these addressed: (i) the frequency and nature of rumination, (ii) cross-sectional relationships between rumination and PTSD symptoms, (iii) the capacity of rumination to predict PTSD longitudinally, (iv) other processes associated with rumination, (v) neurobiological correlates of rumination, and (vi) whether treating PTSD reduces rumination. This review synthesizes these domains of research and identifies key methodological limitations which limit causal inferences, and points to important areas of future research to advance knowledge on rumination in PTSD.

Associations between Trauma Exposure and Physical Conditions among Public Safety Personnel: Associations entre l'exposition à un traumatisme et les problèmes physiques chez le personnel de la santé publique

BACKGROUND

Trauma exposure is associated with adverse health-related correlates, including physical comorbidities, and is highly prevalent among public safety personnel (PSP). The current study (1) examined the association between context of index trauma exposure (part of job vs. other) and physical conditions and (2) established the prevalence of physical conditions according to PSP category (e.g., police, paramedic) and index trauma type (e.g., serious accident, physical assault) in a large Canadian sample of PSP.

METHODS

PSP completed an online survey between September 2016 and January 2017. Multivariable logistic regressions examined associations between context of index trauma exposure (i.e., part of job vs. other) and physical condition categories. Cross-tabulations with chi-square analyses examined whether the prevalence of physical conditions significantly differed according to PSP category and index trauma type.

RESULTS

There were 5,267 PSP included in the current study. Results from the most stringent model of logistic regressions demonstrated that, compared to PSP who experienced their index trauma in any other context, PSP who experienced it as part of their job had reduced odds of "other" physical conditions (adjusted odds ratio = 0.73, 95% confidence interval, 0.57 to 0.94, P < 0.05). Results also revealed significant differences in the prevalence of physical conditions across all PSP categories and select index trauma types.

CONCLUSION

Results highlight the relevance of trauma exposure outside of an occupational context among PSP and may have implications for the positive impact of stress inoculation and resiliency training programs for PSP.

Psychological interventions to foster resilience in healthcare students

BACKGROUND

Resilience can be defined as maintaining or regaining mental health during or after significant adversities such as a potentially traumatising event, challenging life circumstances, a critical life transition or physical illness. Healthcare students, such as medical, nursing, psychology and social work students, are exposed to various study- and work-related stressors, the latter particularly during later phases of health professional education. They are at increased risk of developing symptoms of burnout or mental disorders. This population may benefit from resilience-promoting training programmes.

OBJECTIVES

To assess the effects of interventions to foster resilience in healthcare students, that is, students in training for health professions delivering direct medical care (e.g. medical, nursing, midwifery or paramedic students), and those in training for allied health professions, as distinct from medical care (e.g. psychology, physical therapy or social work students).

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, 11 other databases and three trial registries from 1990 to June 2019. We checked reference lists and contacted researchers in the field. We updated this search in four key databases in June 2020, but we have not yet incorporated these results.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing any form of psychological intervention to foster resilience, hardiness or post-traumatic growth versus no intervention, waiting list, usual care, and active or attention control, in adults (18 years and older), who are healthcare students. Primary outcomes were resilience, anxiety, depression, stress or stress perception, and well-being or quality of life. Secondary outcomes were resilience factors.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, extracted data, assessed risks of bias, and rated the certainty of the evidence using the GRADE approach (at post-test only).

MAIN RESULTS

We included 30 RCTs, of which 24 were set in high-income countries and six in (upper- to lower-) middle-income countries. Twenty-two studies focused solely on healthcare students (1315 participants; number randomised not specified for two studies), including both students in health professions delivering direct medical care and those in allied health professions, such as psychology and physical therapy. Half of the studies were conducted in a university or school setting, including nursing/midwifery students or medical students. Eight studies investigated mixed samples (1365 participants), with healthcare students and participants outside of a health professional study field. Participants mainly included women (63.3% to 67.3% in mixed samples) from young adulthood (mean age range, if reported: 19.5 to 26.83 years; 19.35 to 38.14 years in mixed samples). Seventeen of the studies investigated group interventions of high training intensity (11 studies; > 12 hours/sessions), that were delivered face-to-face (17 studies). Of the included studies, eight compared a resilience training based on mindfulness versus unspecific comparators (e.g. wait-list). The studies were funded by different sources (e.g. universities, foundations), or a combination of various sources (four studies). Seven studies did not specify a potential funder, and three studies received no funding support. Risk of bias was high or unclear, with main flaws in performance, detection, attrition and reporting bias domains. At post-intervention, very-low certainty evidence indicated that, compared to controls, healthcare students receiving resilience training may report higher levels of resilience (standardised mean difference (SMD) 0.43, 95% confidence interval (CI) 0.07 to 0.78; 9 studies, 561 participants), lower levels of anxiety (SMD -0.45, 95% CI -0.84 to -0.06; 7 studies, 362 participants), and lower levels of stress or stress perception (SMD -0.28, 95% CI -0.48 to -0.09; 7 studies, 420 participants). Effect sizes varied between small and moderate. There was little or no evidence of any effect of resilience training on depression (SMD -0.20, 95% CI -0.52 to 0.11; 6 studies, 332 participants; very-low certainty evidence) or well-being or quality of life (SMD 0.15, 95% CI -0.14 to 0.43; 4 studies, 251 participants; very-low certainty evidence). Adverse effects were measured in four studies, but data were only reported for three of them. None of the three studies reported any adverse events occurring during the study (very-low certainty of evidence).

AUTHORS' CONCLUSIONS

For healthcare students, there is very-low certainty evidence for the effect of resilience training on resilience, anxiety, and stress or stress perception at post-intervention. The heterogeneous interventions, the paucity of short-, medium- or long-term data, and the geographical distribution restricted to high-income countries limit the generalisability of results. Conclusions should therefore be drawn cautiously. Since the findings suggest positive effects of resilience training for healthcare students with very-low certainty evidence, high-quality replications and improved study designs (e.g. a consensus on the definition of resilience, the assessment of individual stressor exposure, more attention controls, and longer follow-up periods) are clearly needed.

Prehospital Stressors: A Cross-sectional Study of Norwegian Helicopter Emergency Medical Physicians

OBJECTIVE

Personnel working in helicopter emergency medical services (HEMS) and search and rescue (SAR) are exposed to environmental stressors, which may impair performance. The aim of this survey was to study the extent HEMS and SAR physicians report the influence of specific danger-based and non-danger-based stressors.

METHODS

The study was performed as a cross-sectional, anonymous, Web-based (Questback AS, Bogstadveien 54, 0366 Oslo, Norway) survey of Norwegian HEMS and SAR physicians between December 2, 2019, and February 25, 2020.

RESULTS

Of the recipients, 119 (79.3%) responded. In helicopter operations, 33.6% (n = 40) reported involvement in a minor accident and 44.5% (n = 53) a near accident. In the rapid response car, 26.1% (n = 31) reported near accidents, whereas 26.9% (32) reported this in an ambulance. Of physicians, 20.2% (n = 24) received verbal abuse or threats during the last 12 months. When on call, 50.4% (n = 60) of physicians reported sometimes or often being influenced by fatigue.

CONCLUSION

This study shows that Norwegian HEMS and SAR physicians are exposed to several stressors of both a danger-based and non-danger-based nature, especially regarding accidents, threatening patient behavior, and fatigue. Very serious incidents appear to be seldom, and job satisfaction is high.

Pre-incident Training to Build Resilience in First Responders: Recommendations on What to and What Not to Do

Emergency services are under enormous pressure to offer programmes that could protect their staff from the psychological impact of stressors encountered in their roles. There has been a surge in the number of pre-incident training programmes aimed at first responders to maintain their psychological wellbeing after critical incidents. These include pre-employment screening programmes, psychoeducation, operational training, line manager training and interventions aimed at improving resilience, wellbeing or stress management. Whilst developed with the best intentions, these programmes vary in efficacy. Therefore, knowing what training to offer first responders prior to exposure to critical incidents is far from clear. In this review, we critique the available evidence and make recommendations about what to offer and what to avoid offering first responders prior to exposure to critical incidents. We found no evidence of the effectiveness of pre-employment screening or psychoeducation offered as a standalone package, and little evidence for interventions aimed to improve wellbeing and resilience to stress - although current trials of empirically-driven interventions for first responders are underway and show promise in preventing stress-related psychopathology. Operational and line manager training showed the most promise but need to be evaluated in high quality trials with sufficient follow-up to draw conclusions about their preventative benefits.