Eye Movement Desensitization and Reprocessing:
A Review of the Efficacy of EMDR in the Treatment of PTSD
Louise Maxfield, MA, RCC, CTS
Lakehead University, Canada
Psychology Department

Abstract

The level of evidence for EMDR is based upon twelve controlled studies that investigated the efficacy of EMDR treatment of participants with posttraumatic stress disorder (PTSD). The seven civilian studies, with one exception, all found EMDR to be efficacious in the treatment of PTSD: EMDR was equivalent to cognitive behavioral therapy, and superior to other control conditions. Four of the five studies with combat veterans addressed only one or two memories in this multiply traumatized population, and their findings were equivocal. The one combat veteran study which administered a longer course of treatment provides preliminary evidence that EMDR may be efficacious with that population. EMDR is a rapid treatment and appears to be well tolerated by clients, with effects being maintained at follow-up.


Eye Movement Desensitization and Reprocessing:
A Review of Treatment Efficacy for Posttraumatic Stress Disorder

It has now been more than ten years since Eye Movement Desensitization and Reprocessing (EMDR) was introduced by originator Francine Shapiro (1989). She has described EMDR as "a model, set of principles, procedures and protocols that together represent a new approach to psychotherapy" (1994b, p.155). This treatment method is hypothesized to facilitate the accessing and processing of traumatic memories and to bring these to an adaptive resolution indicated by desensitization of emotional distress, reformulation of associated cognitions, and relief of accompanying physiological arousal. Shapiro (1995, 1999) maintains that EMDR, with its brief exposures to associated material, external/internal focus, and structured therapeutic protocol, is a distinctly different form of therapy, and that it represents a new paradigm in therapy. Because of its claims for rapid effective treatment, EMDR has been subjected to many empirical tests and to much scientific scrutiny. Since Shapiro's (1989) original study, there have been 13 controlled randomized studies that investigated the use of EMDR with participants diagnosed with PTSD. These studies have yielded a range of results, with the efficacy of EMDR varying across studies.

The purpose of the present paper is to review these research studies in an attempt to assess the overall efficacy of EMDR. We begin with a description of the treatment, and then discuss the findings of each study in relation to its strengths and weaknesses. This is followed by a look at the aggregate evidence for EMDRs efficacy in the treatment of PTSD.

The literature is summarized in two sections: The first section includes all seven controlled studies that investigated the efficacy of EMDR treatment of civilian subjects with PTSD; the second section includes all five controlled studies that investigated the efficacy of EMDR treatment of combat veterans with PTSD. In several of the "civilian studies" a small percentage of the subjects were combat veterans. Component studies that used alternate bilateral stimulation for control groups (e.g. Pitman et al., 1996) are not used to evaluate treatment efficacy because they controlled only for one aspect (eye movements) of a complex process, and may not have excluded the possible effective mechanism, which could be focused attention, stimulation of an orienting response, bilateral activation, or rhythmic activity (Shapiro, 1995)

Description of the Treatment Procedure

In EMDR the client focuses on emotionally disturbing material in sequential doses while simultaneously focusing on an external stimulus such as eye movement, hand-tapping or aural stimulation (Shapiro, 1991, 1994a, 1995). This dual (external/internal) focus is combined with frequent brief periods of focusing on new associations as they arise. According to Hyer and Brandsma (1997) and Fensterheim (1996), EMDR is a complex multi-component, multi-staged process, blending many elements of other effective therapies into a comprehensive treatment protocol.

Lohr, Tolin, and Lilienfeld, (1998) suggest that EMDRs effectiveness derives almost entirely from its cognitive behavioral aspects, such as exposure, cognitive restructuring, anxiety desensitization, and breathing. However, EMDR also integrates elements of psychodynamic, body-oriented, person-centered, and interactional therapies (Bohart, in press; Brown, in press; Fensterheim, 1994; Lazarus & Lazarus, in press; Manfield, 1998; Wachtel, in press). Additionally it possesses a number of nonspecific therapeutic components, including therapeutic rapport, client empowerment, and expectations of positive outcome.

Eight Essential Phases

EMDR consists of eight phases, each considered essential for effective application (Shapiro, 1995; Shapiro & Forrest, 1997). EMDR utilizes a direct holistic approach, attending to ongoing affective and physiological changes throughout the session.

During the first two phases the therapist develops a treatment plan, assesses the client's suitability for EMDR, and prepares the client by educating him about the process and teaching him self-control techniques and affect management skills. Client preparation make take several sessions and includes the development of resources and strengths, the establishment of client safety, and stabilization.

In the third phase the client chooses which specific memory he wishes to target, and selects the most distressing visual image connected to that event. The therapist assists him in recognizing the present-day thoughts and feelings that are elicited by the visual image. The client identifies a current negative cognition about himself related to the target memory. Negative cognitions are beliefs such as "I'm powerless", or "I am worthless". Next he chooses a potential positive cognition, which expresses a desired sense of empowerment and agency, such as "I'm competent", or "I have value as a person". He then rates the accuracy of this positive belief on the Validity of Cognition Scale (VOC), where 1 represents "completely false" and 7 represents "completely true".

The client next identifies the emotions that are elicited when the visual image is combined with the negative belief. He rates the level of distress on the Subjective Unit of Disturbance (SUD) scale, where 0 is "calm" and 10 is "the worst possible distress" and identifies and locates the body sensations accompanying the emotions.

The fourth phase is the desensitization phase. The client focuses on the visual image, and the identified negative belief, emotions, and body sensations, while experiencing bilateral stimulation in sequential dosed exposures. The client holds all these elements in mind while simultaneously moving his eyes from side to side for 15 or more seconds, following the therapist's fingers as they move across the visual field. Other bilateral stimuli such as hand-tapping or aural stimulation can replace the eye movements (Shapiro, 1991; 1994b; 1995). After the set of eye movements the client is told to take a deep breath, and then is asked what material was elicited in the process. Generally this material (image, thought, sensation, or emotion) then becomes the target of the next set of eye movements. This cycle of alternating focused exposure and client feedback, is repeated many times and is accompanied by shifts in affect, physiological states, and cognitive insights (e.g., Vaughan et al., 1994). If the processing stalls, specialized interventions are worded and timed in a specific manner to facilitate processing. The SUD level is usually not reassessed until emotional, physical, and cognitive resolution is apparent. A SUD rating of 0 or 1 generally indicates completion of this phase.

In the fifth phase, cognitive installation, the therapist invites the client to pair the previously identified, or an emergent, positive self-statement with the original traumatic image, using bilateral stimulation. The efficacy of this phase is measured by the client's self-reported VOC. An attempt is made to increase the VOC to a score of 6 or 7.

In phase six, the clinician asks the client, while thinking of the image and the positive cognition, to notice if there is any tension or unusual sensations in his body. Because emotional distress is also often experienced physiologically, processing is not considered complete until the client can bring the traumatic memory into consciousness without feeling any body tension. Any sensations found in the body scan are targeted with more eye movements; this continues until the tension is relieved. In phase seven, closure, the therapist assesses that the material has been adequately worked through, and if not, assists the client with self-calming interventions.

Reevaluation (phase eight) takes place at the beginning of every subsequent EMDR session. The therapist checks with the client to assure that the treatment gains have been maintained, via SUD, VOC and body self-report measures. These reevaluations assist the therapist in continuing to direct the treatment to achieve maximum benefit for the client.

Review of the Literature

The first EMD/R study was conducted in 1989 by Shapiro (1989) who randomly assigned 22 combat veterans and civilians to one session of EMD/R or a modified flooding procedure. The subjects were diagnosed with PTSD by referral sources. The measures used consisted of SUD and VOC ratings and a behavioral measure which documented the frequency and severity of the primary presenting complaint (e.g. flashbacks) with corroboration by significant others. Subjects in the EMD/R group showed significant positive treatment effects compared to the control procedure at post-test. Because the modified flooding control subjects showed no improvement, they were provided with EMD/R treatment for ethical reasons. Their response to treatment replicated the results of the first group. These results were independently corroborated at 1- and 3-month follow-up. Shapiro's study (1989) had many limitations. There was no independent blind assessor. The lack of standardized measures prevents the comparison of results with other samples. Provision of EMD/R treatment to the control group eliminated their use as controls for the follow-up measures. Because of the multiple roles played by Shapiro as treatment originator, therapist, and author, experimenter bias cannot be ruled out.

Since 1989, twelve controlled randomized studies have investigated the use of EMDR with PTSD subjects. The methodology has improved and to a greater or lesser extent, later studies have addressed these problems and to provide a more rigorous examination of EMDR. A number of these empirical studies have demonstrated that EMDR is effective as a treatment for PTSD.

Treatment Efficacy Studies with Civilian Participants

EMDR Compared to Wait List Conditions

Rothbaum (1997) randomly assigned 18 adult female rape victims with PTSD to three sessions of EMDR or a wait-list control group. Results were evaluated by a blind independent assessor using structured interviews and self-report measures. The self-report scores of the EMDR participants on PTSD and depression scales showed a mean decrease of more than two standard deviations at post-treatment, which was a significant improvement compared to wait-list controls. Although decreases on other self-report measures were not significant, mean scores of the EMDR group decreased to within normal limits range. At post-treatment, 90% of the subjects in the EMDR group no longer met full criteria for PTSD compared to 12% of the wait-list group. The wait list design is limited: No comparison is made to other treatments and there is no control for nonspecific factors such as therapeutic alliance, expectations, or placebo effects.

Wilson, Becker, and Tinker (1995) randomly assigned a sample of 80 traumatized individuals, 46% of whom were diagnosed with PTSD, to EMDR treatment or Wait List conditions. Each subject received three 90-min sessions of EMDR. A blind independent assessor administered all self-report measures at pre and post treatment and at three month follow-up. Significant differences were found between EMDR and Wait List groups on standardized measures of PTSD symptoms, depression, and anxiety at post-treatment and 3 month follow-up. This improvement was also clinically significant, with the means for all measures moving into a normal range. Treatment gains were strongest for those measures specifically related to trauma. When treatment was provided to the Wait List group, treatment effects were replicated, with significant effects for all measures. A linear regression analysis indicated that treatment gains did not vary as a function of symptom severity or PTSD diagnosis at pre-treatment. This study is limited by its wait list design which does not control for nonspecific treatment factors.

In a 15 month follow-up study (Wilson, Becker & Tinker, 1997), 32 of the original 37 subjects with PTSD were interviewed by an independent assessor. The assessment was not blind as all subjects had received EMDR treatment by this time, and there was no longer a control group. There was an 84% reduction in PTSD diagnosis compared to pre-treatment. Because this design does not control for influences during the 15 month period, such as other treatment or spontaneous remission, it is not possible to conclude that the maintenance of post-treatment outcome resulted solely from EMDR treatment effects.

EMDR Compared to Other Treatments

Marcus, Marquis, and Sakai (1997) compared EMDR to "Standard Kaiser Care" (SKC) in an outpatient HMO. SKC consisted of individual therapy (cognitive, psychodynamic, or behavioral). Sixty-seven individuals with PTSD were randomly assigned to EMDR or SKC treatment. An unspecified number in each group had medication related supervision appointments. Participants received an unlimited number of 50-min treatment sessions; the average number of sessions was not reported. The independent assessor was not blind to treatment condition.

EMDR participants attained symptom reduction with significantly greater rapidity and had significantly fewer treatment sessions and fewer medication related appointments than SKC participants. EMDR produced significantly lower scores than SKC, after 3 sessions and at post-treatment, on measures of PTSD symptoms, depression, and anxiety. After three sessions, 50% of the EMDR participants no longer met the criteria for PTSD, compared to 20% of the SKC group. At post-treatment, 77% of the EMDR group (including 100% of the single trauma victims) no longer met criteria for PTSD compared to 50% of the SKC group. Limitations of this study include the numerous statistical analyses without Bonferroni corrections. Even though the wide variety of treatments used in the control group accurately represents standard care in an HMO setting, their unstandardized heterogeneous nature precludes specific knowledge of their effectiveness for PTSD treatment; this limits the conclusions that can be drawn.

Scheck, Schaeffer, and Gillette (1998) compared EMDR to an active listening (AL) control with a group of 60 traumatized young women who were engaging in high risk behavior such as sexual promiscuity, runaway behavior, or substance abuse. Seventy-seven percent were diagnosed with PTSD using a structured interview. The women received two 90-minute treatment sessions, and had a homework assignment of journal writing. Post treatment measures were collected by an independent blind assessor. No treatment integrity ratings were done.

Both AL and EMDR resulted in significant improvement on all measures, which included measures of PTSD, depression, anxiety, and self-concept. The effects of EMDR were significantly greater than that of AL on all measures except self-concept. This difference was most evident for the most trauma specific measure. Treatment gains were maintained at 3 month follow-up for both groups. Because no assessment was made at post-treatment of the PTSD status of the subjects, it is not known if treatment resulted in a change in PTSD diagnosis. There is no established evidence that active listening is an effective treatment for PTSD, so this study does not compare EMDR to an established effective treatment. The results indicate that EMDR is superior to a condition that controls for some of the nonspecific effects of treatment such as attention, therapeutic rapport, and active listening.

EMDR Compared to Behavioral and Cognitive Behavioral Therapies

Vaughan et al. (1994) assigned 36 participants, 78% of whom were diagnosed with PTSD, to EMD/R, imaginal exposure (IHT), applied muscle relaxation training (AMR), and wait list conditions. The exposure group (IHT) used a procedure in which subjects listened daily for 60-mins to an audiotaped description of their trauma, and recorded thoughts and feelings. Three to five treatment sessions were administered, with daily homework assigned to the IHT and AMR groups only. Blind independent assessments were conducted at pretreatment, post-treatment and at three month follow-up. There were no reported checks on treatment fidelity.

All treatments led to significant decreases in depression and PTSD symptoms for subjects in the treatment groups as compared to those on the wait list. A comparison between treatment groups found a significantly greater reduction at post-treatment for the EMDR group on PTSD intrusive symptoms (IES), and at follow-up for the relaxation group on the BDI. At follow-up, 70% of the PTSD subjects no longer met PTSD diagnostic criteria. Limitations include the limited number of treatment sessions, and different amounts of treatment received by the groups with additional daily homework time in the AMR and IHT groups.

Devilly & Spence (1999) compared EMDR to a treatment developed by Devilly, "Trauma Treatment Protocol" (TTP). TTP has never been examined before, and is a treatment package combining elements of CBT, Stress Inoculation Training, and Prolonged Exposure. Twenty-three civilian subjects with PTSD were randomly assigned to eight sessions of either EMDR or TTP. There was no independent blind assessor. Although treatment integrity was rated as high by an independent EMDR therapist, their description of the technique (Devilly, Spence & Rapee, 1998) indicated a lack of conformity to standardized procedures, with errors such as inaccurate instructions, rating the negative cognition, repeating the negative cognition during treatment, and frequent SUD ratings (see Shapiro, 1995). After the initial information session, 31% of the EMDR participants dropped out before receiving any EMDR treatment.

Both EMDR and TTP were significantly effective on all measures. TTP was significantly more effective than EMDR on combined PTSD measures, and a scale of global function. At three month follow-up, scores on a mailed-in self-report PTSD measure indicated that 58% of the TTP subjects no longer met PTSD criteria compared to only 18% of the EMDR group. Follow-up showed that improvement was maintained with TTP, but worsened with EMDR. Limitations of this study include the large number of statistical analyses done with no Bonferroni correction for Type I error.

Lee and Gavriel (1998) randomly assigned 22 civilian subjects with PTSD to Stress Inoculation Training with Prolonged Exposure (SITPE) or EMDR. They also served as their own controls during a wait list period. Participants were provided with seven 60-min treatment sessions. Measures were collected at pre and post-treatment and at three month follow-up. Assessment was not blind nor independent. Fidelity checks were satisfactory for both treatments.

Both EMDR and SITPE were found to be highly effective, with significant decreases of scores on a PTSD scale and a depression measure. At follow-up 83% of the EMDR subjects and 75% of the SITPE subjects no longer met PTSD criteria. The only difference found between groups was on measures of the Intrusion subscales of the PTSD measures with the EMDR group showing significantly greater improvement. This study indicates that EMDR and SITPE are fairly equivalent in treatment effectiveness. The authors point out that EMDR may be more efficient by not requiring homework assignments. EMDR required an average of 3 hours homework, SITPE required 28 hours.

Summary of the Civilian Studies

Seven controlled studies investigated the efficacy of EMDR with civilian PTSD subjects. The aggregate evidence of the results demonstrates that EMDR is an effective treatment for civilian PTSD. Six of these studies (Lee & Gavriel, 1998; Marcus et al., 1998; Rothbaum, 1997; Scheck et al. 1998; Vaughan et al., 1994; Wilson et al., 1995) found EMDR very effective. These studies indicated that EMDR was superior to active listening, standard Kaiser care, and no treatment, and as effective as CBT. Five of these six studies calculated the decrease in PTSD diagnosis which was substantial, ranging from 70% to 90%. The seventh study (Devilly & Spence) had poor results with EMDR, with only 18% of persons no longer meeting PTSD diagnostic criteria. Although Vaughan et al. and Lee and Gavriel found EMDR and CBT exposure therapies to be relatively equivalent, this was not the finding of Devilly and Spence who found CBT superior. The wide variation in the outcome of these three studies makes apparent the need for further studies to compare EMDR and CBT.

Treatment Efficacy Studies with Combat Veteran Participants

The five controlled studies that examined the efficacy of EMDR treatment of combat veterans with PTSD have shown mixed results. With one exception (Carlson, Chemtob, Rusnak, Hedlund, & Muraoka, 1998) these studies have all been confounded by methodological flaws. First, with the exception of the Carlson et al. (1998) study, the participants were all receiving adjunctive concurrent treatments, confounding the effect of the experimental conditions, and making it impossible to determine unique effects. Second, researchers mistakenly assumed that two or three sessions of EMDR (Boudewyns, Stwertka, Hyer, Albrecht & Sperr, 1993; Devilly, et al., 1998; Jensen, 1994), or addressing just one or two traumatic memories (Boudeywns & Hyer, 1996) would be sufficient to eliminate PTSD in this disabled population. However, combat veterans who experienced multiple traumatic incidents, with a resultant 20 year disability, require comprehensive treatment (Blank, 1993; Scurfield, 1993). Third, the outcome measures used in these studies have been global instruments designed to assess diagnostic status. Focusing therapy on one memory may decrease the distress related to that specific memory, but may not result in a change in diagnostic status for multiply traumatized persons. Studies treating one memory and using only global measures are highly susceptible to Type II error and may fail to find true treatment effects.

Rogers et al. (1999) addressed these issues in a study examining treatment process. They provided a single session of treatment which focused on the most distressing identified combat memory and used measures designed to be sensitive to change on the one treated memory. Twelve combat veterans with PTSD were randomly assigned to EMDR or Exposure. There was a blind independent evaluator and good treatment fidelity.

Rogers et al. found that both groups significantly improved on the IES (as it was applied to that particular memory). A behavioral post-test measure in which subjects monitored the severity of intrusive recollections for the one memory showed a significant decrease for the EMDR group compared to the Exposure group. The purpose of the study was a comparison of therapeutic process, not of treatment efficacy; the results must be considered in this context. This study illustrates the importance of using sensitive and appropriate measures when only one traumatic memory is targeted in subjects with multiple traumas.

Combat Studies Providing Limited Treatment.

Jensen (1994) randomly assigned 25 Vietnam combat veterans suffering from PTSD to a wait list condition or two sessions of EMD/R. No difference was found between groups. Instead of improvement, the condition of the veterans actually deteriorated. Limitations include the use of global measures, lack of blind independent assessment, poor treatment fidelity, insufficient number of sessions and participants receiving concurrent mental health services. The wait list condition was confounded by informing participants that no treatment would be provided and encouraging them to seek treatment elsewhere.

Devilly et al. (1998) assigned 51 combat veterans with PTSD, to one of three conditions: Standard Psychiatric Support (SPS), EMDR, or an EMDR variant (REDDR) in which subjects concentrated on a stationary flashing light. Forty-six percent of the veterans did not mail back their follow-up measures, and the authors note a diminishing of treatment effect over time. Limitations of this study include no blind independent assessment, treatment delivery not according to standard, only one treatment provider, participants receiving concurrent mental health treatment, insufficient number of sessions, and the use of global measures. At post treatment all groups showed significant improvement on measures of PTSD, depression, anxiety, and problem coping. There were no differences between the three groups. Measures of reliable change indicated that 67% of the EMDR group, 42% of the REDDR group, and 10% of the SPS group were reliably improved.

In a pilot study, Boudewyns et al. (1993) provided two sessions of either EMDR or EC (an EMDR analogue with eyes closed) to 20 chronic inpatient veterans who were all receiving standard inpatient treatment. The EMDR group reported significantly less distress elicited by the traumatic memory, but there was no improvement on physiological or standardized global measures for any of the treatments. Limitations include insufficient treatment sessions, global measures, lack of blind independent assessor, no treatment fidelity checks, and concurrent treatment.

Boudewyns and Hyer (1996) sought to evaluate the addition of EMDR to standard group therapy in the treatment of 61 combat veterans with chronic PTSD who were considered multiply disabled and most of whom were receiving disability pensions. Subjects were randomly assigned to one of three conditions: EMDR, an EMDR analogue with eyes closed (EC), or standard group therapy. Every participant received 8 sessions of group therapy, with the EMDR and EC conditions also receiving 5 to 7 treatment sessions of either EMDR or EC. Participants in all three conditions improved significantly on a structured interview measuring PTSD symptoms, with no group differences. Subjects in the EMDR analogue (EC) and EMDR conditions showed superior improvement on a mood and physiological measures compared to group therapy controls. This study indicates that the addition of EMDR or EC to group treatment may improve outcome. Boudewyns and Hyer report that both therapists and clients preferred EMDR to the more direct exposure condition (EC). Limitations include the treatment of only one or two memories, use of global measures, variable treatment fidelity, and subjects receiving concurrent group treatment.

Combat Studies Providing Full Treatment

Only one EMDR study has provided a full course of treatment for combat veterans with PTSD. Carlson et al. (1998) randomly assigned 35 Vietnam combat veterans to a wait list control, or to 12 treatment sessions of biofeedback relaxation, or EMDR. At post-treatment, the EMDR group had significantly lower scores on instruments measuring PTSD and depression than the wait list. At 3-month follow-up, EMDR had significantly lower scores than the biofeedback relaxation group on measures of PTSD and self-reported symptoms. Both treatment groups and the wait list control showed significant improvement on physiological measures with no differences between groups. This decrease in physiological arousal was maintained at 3 month follow-up. Nine of the ten EMDR subjects completed the 9 month follow-up which confirmed the maintenance of treatment effects. Seventy-eight percent of the EMDR subjects no longer met the diagnostic criteria for PTSD. This study controls for the often neglected variable of therapist allegiance (Hollon, 1999), as the non-EMDR subjects received the treatment to which the therapist had allegiance. Because biofeedback relaxation therapy has not been designated an efficacious treatment for PTSD, it could be argued that this study does not compare EMDR to another acknowledged effective treatment, but only controls for some of the nonspecific effects of treatment.

Summary of EMDR Studies with Combat Veteran Participants

Five controlled studies have examined the efficacy of EMDR with combat veterans. This research area has suffered from poor methodology. In four studies (Boudewyns et al.,1993; Boudewyns & Hyer, 1996; Devilly, et al., 1998; Jenson, 1994), subjects were provided with only two or three treatment sessions, or addressed only one or two of multiple traumatic memories. Treatment outcome was assessed by determining if there was change in PTSD diagnosis. Also the participants in these four studies were all receiving adjunctive concurrent treatments, confounding the effect of the experimental conditions, and making it impossible to determine unique effects. Although some changes in diagnostic status were found (Boudewyns & Hyer, 1996; Devilly et al, 1998) because of the methodological limitations, these four studies provide no clear evidence of the effectiveness of EMDR with combat PTSD. In the fifth study (Carlson et al., 1998) an adequate number of treatment sessions was provided, the methodology was sound, and EMDR resulted in positive treatment effects with indication of superiority to a wait list condition and to biofeedback relaxation. Carlson et al. (1998) found that 78% of the EMDR subjects no longer met the diagnostic criteria for PTSD at follow-up. This study, and the process study by Rogers et al. (1999), provide preliminary evidence that EMDR may be efficacious in the treatment of combat veterans with PTSD. More research is needed with this population.
 
 
 

The Aggregate Evidence for EMDRs Efficacy in the Treatment of PTSD

The results of six of the civilian studies and one of the combat veteran studies suggest that EMDR is an effective therapy for PTSD. It appears to be more effective than active listening, standard Kaiser care, relaxation therapy and no treatment. There are preliminary indications that it may be equivalent in effectiveness to CBT exposure therapies.

EMDR had the largest influence on measures of PTSD symptoms, with fairly consistent improvement across the civilian studies. Improvement on measures of other types of symptoms such as depression were not as robust, and varied within and between studies. Most studies offered only a few treatment sessions and it may be that more distressed clients would have benefitted from additional sessions. More distressed clients may also have more comorbid disorders. Wilson et al. (1997) found that those clients reporting higher levels of distress at 3-month follow-up were the most likely to seek further treatment over the next year.

Persons who have suffered multiple traumas, such as combat veterans, may require more extensive therapy. Marcus et al. (1997) reported that EMDR resolved PTSD more rapidly for those clients with a single trauma. The only combat veteran study which provided extensive treatment was the only one that achieved positive treatment outcome (Carlson et al., 1998). This suggests that research evaluating EMDR treatment of chronic PTSD must provide a full course of therapy to adequately assess efficacy.

Another issue that may explain the range of outcomes across studies is methodological rigor. The civilian study which reported a poor outcome (Devilly & Spence, 1999) and several of the combat veteran studies were limited by various methodological flaws, which may have obscured true treatment effects. It appears that differences in outcome are related to differences in methodology, and that higher ratings of methodological rigor predict treatment effect sizes (Maxfield & Hyer, in press).

Further research is required to examine the responses of different PTSD populations to EMDR treatment. At present the research indicates that EMDR is effective for civilian PTSD. Only tentative conclusions can be reached concerning EMDRs effectiveness for combat PTSD until further research replicates studies like Carlson et al. (1998) and compares EMDR with other effective treatments for combat PTSD. Research should evaluate individual response to EMDR to determine if there are differential effects for persons with comorbid disorders, multiple traumas, or with chronic PTSD.
 
 
 

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