EMDR FORUM ARCHIVE, 2000
Re:Maxfield & Hyer meta-analysis: A few questions
Cahill · 11/13/02 at 4:25 PM ET
Follow-up data were presented in the original Marks et al. (1998) paper. All groups displayed further improvement during follow-up period. The problem is the increasing rate of drop out as the follow-up period went on, raising the possiblity that the change seen in follow-up is not representative of the whole group. This problem is not unique to the Marks et al. study. Regarding the Powers et al. study, nobody to my knowledge has questioned the credentials of those adminstering the treatments. I don't think you are under attack here. Whether or not the Powers et al. results suggest that exposure and EMDR operate through different mechanisms is still open to discussion. At present, we've got the Vaughan et al. study that found EMDR, image habituation training (IHT; a somewhat unusual form of exposure therapy), and relaxation to be roughly equivalent. Devilly and Spence found exposure therapy plus anxiety management plus cognitive therapy was superior to EMDR, but there are some issues about randomization. The Ironson et al. study found EMDR plus in vivo exposure to be the same as imaginal exposure plus in vivo exposure. They argue that there is some evidence that EMDR was more efficient, but I believe this was an artifact of the exposure therapy being numerically higher at pre-treatment than the EMDR group. The amount of change after three prep sessions and three treatment sessions was nearly identical for the two treatments. However, the percent change in EMDR was greater. Mathematically, the only way for this to be true is if the denominator of the percent ratio (the pretreatment score in this case) for EMDR was smaller than for exposure therapy. Specifically, the average pretreatment PSS-SR score for exposure was 34.56, the average posttreatment score was 15.78, resulting in an 18.78 point change, which translates to an average 54.3 percent reduction. In EMDR, the pretreatment score was 26.58 and the posttreatment score was 9.1, for a mean reduction of 17.48 points, which is numerically SMALLER than the reduction for exposure therapy, but it translates to an average of 65.8 percent change. Therefore, I don't believe their conclusions about efficiency are warrented and that both treatments were roughly equivalent. Then we have Lee et al. and Powers et al. suggesting some evidence for superiority of EMDR. But there are still two studies whose results have been presented at conferences, but the final reports are not published. I've seen Barbara Rothbaum present her data last year at AABT and at ADAA. The results suggested statisitical comparability, but numerical superior for exposure therapy. I didn't see Steve Taylor's presentation at the World Congress and only heard the results second hand. Therefore, I will refrain from commenting on them. So, two general comments: 1. Not all the relevent data are yet in, so it may be appropriate to withold judgement or to at least be tentative. 2. The results of published studies to date are a mixed bag, with one clearly in favor of CBT (D & S), two ties (Vaughan et al., Ironson et al.), two favoring EMDR (Lee et al., Powers et al.), and we stand by with bated breath on two studies (Rothbaum and Taylor).
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