Psychiatric Annals

CME Article 

Psychological Interventions to Prevent PTSD

Sara A. Freedman, PhD

Abstract

Experiencing a traumatic event is ubiquitous, whereas developing posttraumatic stress disorder (PTSD) is less likely. However, PTSD can become a chronic and disabling disorder, making primary and secondary prevention important goals. Studies have shown that we know little about preventing PTSD before the traumatic event has happened. In the first hours after the traumatic event, psychological debriefing is likely to have no or potentially a negative effect on subsequent PTSD and psychological interventions have not shown consistent results. Providing common-sense help and reassurance is likely to be helpful. In the first weeks or months after the traumatic event, providing cognitive-behavioral therapy (CBT) for highly symptomatic patients is helpful in preventing PTSD. When resources are not immediately available, waiting for up to 3 months before starting CBT gives similar long-term results. [Psychiatr Ann. 2019;49(7):314–319.]

Abstract

Experiencing a traumatic event is ubiquitous, whereas developing posttraumatic stress disorder (PTSD) is less likely. However, PTSD can become a chronic and disabling disorder, making primary and secondary prevention important goals. Studies have shown that we know little about preventing PTSD before the traumatic event has happened. In the first hours after the traumatic event, psychological debriefing is likely to have no or potentially a negative effect on subsequent PTSD and psychological interventions have not shown consistent results. Providing common-sense help and reassurance is likely to be helpful. In the first weeks or months after the traumatic event, providing cognitive-behavioral therapy (CBT) for highly symptomatic patients is helpful in preventing PTSD. When resources are not immediately available, waiting for up to 3 months before starting CBT gives similar long-term results. [Psychiatr Ann. 2019;49(7):314–319.]

After a multivehicle collision, 20 patients are admitted to the emergency department (ED). There were fatalities in the collision, and family members arrived at the ED to comfort their loved ones. Apart from the physical injuries, many patients are distressed, some are confused, and others belligerent. All are at potential risk for developing posttraumatic stress disorder (PTSD). What is the best strategy to provide immediate relief? Can longer-term disorders be prevented? What is the best approach to these patients and their families in the hours, days, and weeks after the event, and how likely is it to help in preventing the development of posttraumatic stress disorder? This article addresses psychological treatments studied as a prevention of PTSD, and are summarized in Table 1.

Preventing PTSD: A Summary

Table 1:

Preventing PTSD: A Summary

Posttraumatic Stress Disorder

Approximately 90% of the population will be exposed to a potentially traumatic event during their lifetime and thus will be at risk of developing PTSD, a disorder with a lifetime prevalence of 8%.1 The PTSD diagnostic template includes symptoms of re-experiencing (such as intrusive memories of the event), avoidance (of reminders of the event), negative affect, and arousal (for instance startle response). PTSD co-occurs with several psychiatric disorders such as major depression, substance misuse, and anxiety disorders as well as with marital difficulties, child-rearing problems, unemployment, suicide, and health problems.2 Family members of patients with PTSD are also more likely to report psychiatric and other symptoms. As such, chronic PTSD represents a public health challenge.2

Most people who are exposed to a traumatic event will express transient PTSD symptoms in the first days and weeks after the event, but those will likely disappear over time.3 Such natural recovery occurs without intervention, and continues over the first year, after which lower recovery rates are found. This course is particularly important as it implies that none of the distressed patients in the ED of our illustrative case example is expressing symptoms of a psychological disorder; however, acute reactions to a stressful situation are expected to subside in more than 70% of those initially expressing them.4

Nonetheless a significant minority of these individuals who have experienced a traumatic event (eg, 18% of road traffic accidents; 38% of terror survivors)5 will continue to express distressing and disabling PTSD symptoms in the months after trauma exposure. Therefore, despite natural recovery, the occurrence of persistent PTSD, delayed help seeking, and partial responses to treatment emphasize the need for a proactive approach for early interventions that can prevent PTSD; in this article, we outline, using a chronological path, interventions preceding the traumatic event (alias “primary prevention”) to interventions in the immediate aftermath of trauma to those provided weeks or a few months after trauma exposure.

Primary Prevention of PTSD

Primary prevention assumes that providing interventions before potential exposure can reduce the likelihood of PTSD development. Although there are wide-ranging accounts of psychological resilience training, and more recently neurobehavioral training techniques, few of these have been sufficiently evaluated as specific PTSD prevention techniques. Some studies report decreased PTSD and other symptoms after exposure to a traumatic event in those that received a pre-trauma intervention.6 Some studies have not included baseline evaluations, or a proper assessment of trauma exposure,7 although more recent controlled studies have shown that threat attention modification before combat exposure is related to less PTSD postdeployment.8

Secondary Prevention of PTSD: Rationale

The rationale for psychological prevention of PTSD is broadly based on the theoretical concept of emotional processing.9 This posits that to successfully cope with a traumatic event and the inevitable symptoms that accompany it, a process of change is needed. Successful recovery is accomplished, most often without intervention, when the person can integrate information and experiences related to the traumatic event with previously held experiences, worldviews, expectations, beliefs, and with postexposure changes (eg, loss, injury).

For instance, someone involved in the aforementioned fatal car crash is likely to have difficulty sleeping and concentrating, be fearful and sad, and spend time thinking about the accident in the days after the accident. If a person who was involved in the crash starts avoiding traveling in cars, tries not to think about the crash, and blames himself or herself for being sad, it will be a challenge to integrate the new information acquired during the crash (eg, “I could have died”; “It was really scary”; “I can lose control of myself”) with pre-existing worldviews (eg, “I generally cope well with trauma”; “Driving is generally safe”) and other information (its normal to be scared and sad; not all journeys in a car lead to a fatal car crash; my friends are very supportive).

Different theoretical standpoints put more emphasis on different parts of this model (eg, the role of avoidance; the importance of negative cognitions; the salience of social relationships), but the common factor is the understanding that PTSD development represents an impairment of psychological recovery processes.10 This understanding is pivotal to assuming that people can be taught techniques to facilitate recovery and that such learning can prevent PTSD.

Another focus of PTSD prevention rationale regards the role of traumatic memories. These may differ from nontraumatic memories in that they remain encoded as incomplete, sensory, and disorganized recollections. Avoidance (of thinking about the event, of emotions regarding the event) makes shifting such memories to more controllable episodic memories difficult.9 Studies have also demonstrated the importance of traumatic memories by showing that people with little memory of the event are less likely to develop PTSD.11 Thus, recovery may be facilitated if the trauma memory can be elaborated, or if the consolidation of traumatic memories can be interrupted.12

Psychological Interventions in the First Hours and Days After Trauma-Exposure

Well-controlled studies examining interventions in the first hours posttrauma are rare, and this probably reflects the challenges of working in the immediate aftermath of a traumatic event. The victims involved in our illustrative case example are likely to undergo physical examinations and care for injuries and are likely to present with a range of psychological reactions. One appropriate path at this stage is a common-sense approach such as Psychological First Aid (PFA),11 which includes promoting safety, a feeling of calmness, and helping with connectedness, self-efficacy, and hope. In practice, PFA might include helping the car crash survivors in the illustrative case to call and connect with their family members, check that they have somewhere to sleep and a means to get there, provide a link to helping agencies, and provide a link for continuity of care if needed. PFA has shown to reduce distress at this stage.13

Studies that have examined interventions in the immediate hours after a traumatic event include interventions aimed at helping survivors create a better organized memory of the event,14 preventing consolidation of the traumatic memory,15 and a modified prolonged exposure intervention.16 Overall, these studies have not shown consistent results and thus psychological interventions provided immediately after exposure cannot be recommended at this stage.

Prevention studies conducted in the first days after the traumatic event have mainly used psychological debriefing,17 in which people are asked to provide detailed facts of what happened, including their thoughts, reactions, and symptoms, and are provided with psychoeducation about symptoms and how to deal with them. Studies examining debriefing as a secondary prevention have most often used it as a one-off group intervention (eg, one session) without prior assessment and diagnosis. Controlled trials have shown that debriefing has no effect in preventing PTSD and might result in a greater likelihood of developing PTSD. Thus, the use of psychological debriefing (one-off intervention) to prevent PTSD is not supported by evidence.18

Psychological Interventions in the First Weeks After Exposure

Studies performed within this timeframe have mainly compared cognitive-behavioral therapy (CBT) with treatment as usual, a waitlist control, or have compared different types of CBT.19 Some of these interventions have been brief or shortened versions of protocols used with chronic PTSD (5–6 sessions), whereas others included 12 to 16 sessions.

Most CBT interventions involve elements such as psychoeducation regarding PTSD and common reactions to traumatic events; breathing retraining; addressing avoidance symptoms using gradual in vivo exposure to real-life situations (eg, going back to the site of the traumatic event, getting into or riding a bus); imaginal exposure, where the patient re-tells the story of the event to help with memory processing; and challenging unhelpful and inaccurate cognitions acquired after the event and concerning oneself (eg, incompetent, coward), the world around (hostile, dangerous), or the probability of future trauma.20

Results from randomized controlled studies indicate that CBT that includes exposure-based strategies is effective at preventing PTSD. For instance, an early study showed that a 5-week prolonged exposure intervention for people with acute stress disorder was more effective than supportive counseling.21 A larger study showed that 12 weeks of prolonged exposure was equally effective as cognitive therapy in preventing PTSD.22 This study also showed that providing intervention at 4 months posttrauma gave the same results at follow-up as earlier treatment.

Several conclusions can be drawn from these studies. First, the provision of CBT is generally associated with levels of PTSD lower than those of control conditions21 and this effect is stable over time.23 CBT, however, is no better than natural recovery in people who do not meet PTSD diagnostic criteria.23 Exposure-based interventions, in which participants directly confront their avoidance of memories and situations reminding them of the trauma, have been hailed as more efficient than those that only include cognitive elaboration in some21 but not all23 studies.

Importantly, some survivors do not respond to early CBT and about 1 in 4 stops treatment prematurely.24 The reasons for not responding have not been clarified and we currently have no reliable way to predict early CBT responses. Clinical experience suggests that some trauma survivors may require preparation before starting exposure-based CBT to ensure better understanding of the task ahead and identify problems and issues (eg, concurrent stressors) that might reduce treatment efficacy but at this point there are no data supporting the advantage of such practices. As such, CBT should not be separated from overall trauma survivorship management and seen as working regardless of personal and social context.

Other early interventions deemed efficacious in reducing PTSD symptoms, but not having the depth of CBT research include a dyadic intervention, which includes facilitating communication with a significant other,25 and an Eye Movement Desensitization and Reprocessing (EMDR) Protocol for Recent Critical Incidents, which includes sessions on 2 consecutive days.26

Overall, trauma-focused CBT is the recommended option in the early weeks posttrauma for patients who are symptomatic.27 When resources are scarce, or when patients are unable to attend treatment that early after the event (for instance because they are occupied with more basic needs after a natural disaster), then providing treatment at 3 months gives the same long-term effects.28

Internet-Based Early Interventions

People are often reluctant to attend treatment, and alternative platforms for providing treatment may overcome some of these barriers. In particular, the use of Internet-based interventions has become more established in recent years. A small number of studies have examined CBT-based Internet prevention programs, and these show mixed results, both in terms of uptake and differences at follow-up.29

Diagnosis and Symptoms Levels

Some early interventions have been designed for a whole population, either those who have risk factors for experiencing a traumatic event or those who have experienced a traumatic event. Others have attempted to screen and assess people before deciding whether they need intervention.30 The results of these studies are consistent, showing that interventions provided to whole populations do not show beneficial results, whereas trauma-focused CBT provided to patients who are symptomatic can prevent PTSD. Meta-analysis of these studies concludes that “evidence of the benefits of trauma-focused CBT for symptomatic individuals who did not meet full diagnostic criteria for these conditions was weak.”23

Conclusions

Natural recovery is the most frequent outcome of trauma exposure and early interventions must be better than natural recovery to be acceptable and ethical. As can be seen,31 psychological debriefing can result in worse outcomes than natural recovery and should be avoided. Interventions that are aimed at all people who have been exposed to trauma are not superior than natural recovery. Persisting PTSD symptoms and an early diagnosis of PTSD are the plausible prerequisites for systematic interventions. Recently published treatment guidelines27 indicate that multisession CBT (of different types) is recommended as a prevention of PTSD, and EMDR has emerging evidence of efficacy. Other psychological interventions (eg, computerized neurobehavioral training, internet virtual reality therapy, supportive counseling, or telephone-based CBT32) even when given only to those with justifying early symptoms may not be superior to natural recovery.

Clinicians should nonetheless be aware that the sources of current evidence-based knowledge are mainly controlled studies33,34 using mean changes of symptom levels and evaluating survivors under controlled experimental conditions. As such they do not properly estimate response heterogeneities and have seldom addressed extreme traumatic conditions (eg, gang rape, school or crowd shooting) or prolonged adversities (eg, captivity and torture). Keeping that in mind, and acknowledging the demonstrated advantage of early CBT, clinicians should use their best judgement in individual cases. For example, a study of ED-initiated CBT16 reported symptom improvement in rape victims but not in accident survivors, and such information should encourage using clinicians' expertise and early assessment in adjudicating treatment needs. Most importantly, the general principles of approaching survivors who are traumatized apply regardless of interventions' specifics: create a safe environment and help patients reach safety; obtain survivors' trust and provide interventions within a larger context of understanding survivors' postexposure needs, concerns, expectations and beliefs; and, as often is the case, educate and include survivors significant others' as supportive and understanding helpers.

Returning to our illustrative case example, what is the best way to proceed with the victims of the car crash? In the ED, providing PFA is likely to be helpful, which includes making sure that patients are oriented and have the immediate resources to deal with the situation, reducing sources of current distress, and providing them with some measure of control over their situation and consequent decisions. Further interventions in the ED are not clearly recommended. In the best-case scenario, ED patients, particularly those who have survived events involving death, disfiguration, or blunt interpersonal violence (eg, rape, torture) and those showing extreme or perturbing “peritraumatic” symptoms (eg, dissociation, agitation), would be proactively observed once they have left the ED, and that those showing all the symptoms of PTSD within 1 month would be offered CBT. With limited resources, observing those patients who have risk factors should be prioritized. A recent analysis suggests that women with lower education and prior exposure to interpersonal trauma may be most at risk.32 For those unable or unwilling to attend therapy, the potential for Internet-based interventions is a possibility. Most of the 20 people in our illustrative case example will recover naturally. For the 4 or 5 who show lingering PTSD symptoms, CBT offers the best possibility of preventing PTSD.

References

  1. Kessler RC, Aguilar-Gaxiola S, Alonso J, et al. Trauma and PTSD in the WHO World Mental Health Surveys. Eur J Psychotraumatol. 2017;8(suppl 5):1353383. doi:. doi:10.1080/20008198.2017.1353383 [CrossRef]
  2. Kessler RC. Posttraumatic stress disorder: the burden to the individual and to society. J Clin Psychiatry. 2000;61(suppl 5):4–12.
  3. Mouthaan J, Sijbrandij M, Luitse JS, Goslings JC, Gersons BPR, Olff M. The role of acute cortisol and DHEAS in predicting acute and chronic PTSD symptoms. Psychoneuroendocrinology. 2014;45:179–186. doi:. doi:10.1016/j.psyneuen.2014.04.001 [CrossRef]
  4. Shalev AY, Freedman S, Peri T, et al. Prospective study of posttraumatic stress disorder and depression following trauma. Am J Psychiatry. 1998;15(5):630–637. doi:. doi:10.1176/ajp.155.5.630 [CrossRef]
  5. Shalev AY, Freedman S. PTSD following terrorist attacks: a prospective evaluation. Am J Psychiatry. 2005;162(6):1188–1191. doi:. doi:10.1176/appi.ajp.162.6.1188 [CrossRef]
  6. Wolmer L, Hamiel D, Laor N. Preventing children's posttraumatic stress after disaster with teacher-based intervention : a controlled study. J Am Acad Child Adolesc Psychiatry. 2011;50(4):340–348. doi:. doi:10.1016/j.jaac.2011.01.002 [CrossRef]
  7. Skeffington PM, Rees CS, Kane R. The primary prevention of PTSD: a systematic review. J Trauma Dissociation. 2013;14(4):404–422. doi:. doi:10.1080/15299732.2012.753653 [CrossRef]
  8. Wald I, Fruchter E, Ginat K, et al. Selective prevention of combat-related post-traumatic stress disorder using attention bias modification training: a randomized controlled trial. Psychol Med. 2016;46(12):2627–2636. doi:. doi:10.1017/S0033291716000945 [CrossRef]
  9. Brewin CR, Holmes EA. Psychological theories of posttraumatic stress disorder. Clin Psychol Rev. 2003;23(3):339–376. doi:. doi:10.1016/S0272-7358(03)00033-3 [CrossRef]
  10. Resick PA, Monson CM, Chard KM. Cognitive Processing Therapy for PTSD: A Comprehensive Manual. New York, NY: Guilford Press; 2017.
  11. Glaesser J, Neuner F, Lütgehetmann R, Schmidt R, Elbert T. Posttraumatic stress disorder in patients with traumatic brain injury. BMC Psychiatry. 2004;4:5. doi:. doi:10.1186/1471-244X-4-5 [CrossRef]
  12. Iyadurai L, Visser RM, Lau-Zhu A, et al. Intrusive memories of trauma: a target for research bridging cognitive science and its clinical application. Clin Psychol Rev. 2019;69:67–82. doi:. doi:10.1016/j.cpr.2018.08.005 [CrossRef]
  13. Forbes D, Lewis V, Varker T, et al. Psychological first aid following trauma: implementation and evaluation framework for high-risk organizations. Psychiatry. 2011;74(3):224–239. doi:. doi:10.1521/psyc.2011.74.3.224 [CrossRef]
  14. Gidron Y, Gal R, Freedman S, Twiser I, Lauden A, Snir Y, Benjamin J. Translating research findings to PTSD prevention: results of a randomized-controlled pilot study. J Trauma Stress. 2001;14(4):773–780. doi:. doi:10.1023/A:1013046322993 [CrossRef]
  15. Horsch A, Vial Y, Favrod C, et al. Reducing intrusive traumatic memories after emergency caesarean section: a proof-of-principle randomized controlled study. Behav Res Ther. 2017;94:36–47. doi:. doi:10.1016/j.brat.2017.03.018 [CrossRef]
  16. Rothbaum BO, Kearns MC, Price M, et al. Early intervention may prevent the development of posttraumatic stress disorder: a randomized pilot civilian study with modified prolonged exposure. Biol Psychiatry. 2012;72(11):957–963. doi:. doi:10.1016/j.biopsych.2012.06.002 [CrossRef]
  17. Rose S, Bisson J, Churchill R, Wessely S. Psychological debriefing for preventing post traumatic stress disorder (PTSD). Cochrane Database Syst Rev. 2002;(2):CD000560. doi:10.1002/14651858.CD000560 [CrossRef].
  18. Kearns MC, Ressler KJ, Zatzick D, Rothbaum BO. Early interventions for PTSD: a review. Depress Anxiety. 2012;29:833–842. doi:. doi:10.1002/da.21997 [CrossRef]
  19. Birur B, Moore NC, Davis LL. An evidence-based review of early intervention and prevention of posttraumatic stress disorder. Commun Ment Health J. 2017;53(2):183–201. doi:. doi:10.1007/s10597-016-0047-x [CrossRef]
  20. Watkins LE, Sprang KR, Rothbaum BO. Treating PTSD: a review of evidence-based psychotherapy interventions. Front Behav Neurosci. 2018;12:258. doi:. doi:10.3389/fnbeh.2018.00258 [CrossRef]
  21. Bryant RA, Sackville T, Dang ST, Moulds M, Guthrie R. Treating acute stress disorder: an evaluation of cognitive behavior therapy and supportive counseling techniques. Am J Psychiatry. 1999;156(11):1780–1786. doi:10.1176/ajp.156.11.1780 [CrossRef].
  22. Shalev AY, Ankri Y, Israeli-Shalev Y, Peleg T, Adessky R, Freedman S. Prevention of posttraumatic stress disorder by early treatment: results from the Jerusalem trauma outreach and prevention study. Arch Gen Psychiatry. 2012;69(2):166–176. doi:. doi:10.1001/archgenpsychiatry.2011.127 [CrossRef]
  23. Roberts NP, Kitchiner NJ, Kenardy J, Bisson JI. Systematic review and meta-analysis of multiple-session early interventions following traumatic events. Am J Psychiatry. 2009;166(3):293–301. doi:. doi:10.1176/appi.ajp.2008.08040590 [CrossRef]
  24. Bryant RA, Mastrodomenico J, Felmingham KL, et al. Treatment of acute stress disorder: a randomized controlled trial. Arch Gen Psychiatry. 2008;65(6):659–667. doi:. doi:10.1001/archpsyc.65.6.659 [CrossRef]
  25. Brunet A, Des Groseilliers IB, Cordova MJ, Ruzek JI. Randomized controlled trial of a brief dyadic cognitive-behavioral intervention designed to prevent PTSD [published online ahead of print August 26, 2013]. Eur J Psychotraumatol. doi:10.3402/ejpt.v4i0.21572 [CrossRef].
  26. Jarero I, Uribe S, Artigas L, Givaudan M. EMDR protocol for recent critical incidents: a randomized controlled trial in a technological disaster context. J EMDR Pract Res. 2015;9(4):166–173. doi:. doi:10.1891/1933-3196.9.4.166 [CrossRef]
  27. International Society for Traumatic Stress Studies. New ISTSS prevention and treatment guidelines. https://www.istss.org/treating-trauma/new-istss-guidelines.aspx. Accessed May 29, 2019.
  28. Shalev AY, Ankri Y, Gilad M, et al. Long-Term outcome of early interventions to prevent posttraumatic stress disorder. J Clin Psychiatry. 2016;77(5):e580–e587. doi:. doi:10.4088/JCP.15m09932 [CrossRef]
  29. Ennis N, Sijercic I, Monson CM. Internet-delivered early interventions for individuals exposed to traumatic events: systematic review. J Med Internet Res. 2018;20(11):e280. doi:. doi:10.2196/jmir.9795 [CrossRef]
  30. Brewin CR, Fuchkan N, Huntley Z, et al. Outreach and screening following the 2005 London bombings: usage and outcomes. Psychol Med. 2010;40(12):2049–2057. doi:. doi:10.1017/S0033291710000206 [CrossRef]
  31. Agorastos A, Marmar CR, Otte C. Immediate and early behavioral interventions for the prevention of acute and posttraumatic stress disorder. Curr Opin Psychiatry. 2011;24(6):526–532. doi:. doi:10.1097/YCO.0b013e32834cdde2 [CrossRef]
  32. Shalev AY, Gevonden M, Ratanatharathorn A, et al. Estimating the risk of PTSD in recent trauma survivors: results of the International Consortium to Predict PTSD (ICPP). World Psychiatry. 2019;18(1):77–87. doi:. doi:10.1002/wps.20608 [CrossRef]
  33. Bryant RA, Sackville T, Dang ST, Moulds M, Guthrie R. Treating acute stress disorder : an evaluation of cognitive behavior therapy and supportive counseling techniques. Am J Psychiatry. 1999;156(11):1780–1786. doi:10.1176/ajp.156.11.1780 [CrossRef].
  34. Shalev AY, Ankri Y, Israeli-Shalev Y, Peleg T, Adessky R, Freedman S. Prevention of posttraumatic stress disorder by early treatment: results from the Jerusalem Trauma Outreach And Prevention study. Arch General Psychiatry. 2012;69(2):166–176. doi:. doi:10.1001/archgenpsychiatry.2011.127 [CrossRef]
  35. Shultz JM, Forbes D. Psychological first aid. Rapid proliferation and the search for evidence. Disaster Heal. 2014;2(1):3–12. doi:. doi:10.4161/dish.26006 [CrossRef]

Preventing PTSD: A Summary

Intervention Description Efficacy in Preventing PTSD Level of Evidence
Resilience training7 Stress inoculation training provided to group with risk factors before exposure to trauma Some reports show reduced PTSD levels Low
Psychological First Aid35 Common sense help in first hours posttrauma Evidence informed Low
Psychological debriefing17 Survivors asked to repeat the narrative of their traumatic event in the first hours or days posttrauma; individual or group setting None or negative Good
Exposure-based CBT27 Individual therapy, including psychoeducation, breathing retraining, in vivo exposure to avoided situation, imaginal exposure to narrative of the trauma, cognitive restructuring Efficient in survivors with full PTSD symptoms Good
Supportive counseling27 Problem-solving skill, general support Significantly less effective than CBT Good
Internet-based CBT29 CBT skills, as above, provided on the Internet, either with or without therapist support None in adults; helpful in children Low
Authors

Sara A. Freedman, PhD, is an Associate Professor, School of Social Work, Bar-Ilan University.

Address correspondence to Sara A. Freedman, PhD, School of Social Work, Bar-Ilan University, Ramat-Gan, 5290002 Israel; email: Sara.freedman@biu.ac.il.

Disclosure: The author has no relevant financial relationships to disclose.

10.3928/00485713-20190528-01

Sign up to receive

Journal E-contents