EMDR FORUM ARCHIVE, 2000
Re:Maxfield & Hyer meta-analysis: A few questions
Cahill · 11/03/02 at 5:07 PM ET
Louise: You state that you hope that I'm not "aking the cognitive error of assuming that all persons who speak positively about EMDR ascribe to the same set of beliefs and behaviors." I can't for the life of me see where this comment is comming from. If you look back over my posts, I believe you will see that I make a concerted effort to attribute specific positions to specific people, or I use qualified terms like "some proponents of EMDR" ect. In fact, just two posts back I was juxtaposing what I thought were contradictory positions, one advanced by you and the other inferred from Sandra's writing. In that post, I explicitly acknowledged that the two of you may have different views: "Now, I realize I'm carrying on conversations with different people, and that Sandra may not endorse the strong methodological position that Louise advanced." Regarding your position of treatment fidelity as internal validity, fine. I have no qualms with that. I just would like the point to applied equally so that when Shapiro or anyone else claims to have made improvements, in the absence of data to demonstrate this, we should openly acknowledge they are violating the treatment protocol and any results are irrelevant to EMDR per se. Regarding your role in the Taylor PTSD study, I am quite aware of your participation and I look forward to seeing the published results. Are you in any position to share the outcome with the forum? Regarding the Marks et al. study, it is true that cogntive therapy was equivalent to exposure therapy. I don't think I represented things otherwise. Tarrier et al. found the same thing, although he handicapped both treatments: in vivo exposure was removed from exposure therapy and behavioral experiments were removed from cognitive therapy. This was done to remove overlap between the two treatments. Results in both studies were roughly equivalent. Interestingly, one of Marks' colleagues, Lovell I believe (I can provide the citation latter, as the paper is it work and I'm at home), published a secondary analysis of that study investigating the hypothesis that there would be differential effects of the treatments on different PTSD symptom clusters. They predicted on theoretical grounds that cognitive therapy would have greater effect on certain symptoms and that exposure therapy would have greater effect on other symptoms. Of course, one would expect the combined treatment to get the best of both worlds (again, I can't recall how they mapped the different subscales onto the different treatments. I can post those details tomorrow). The results found all conditions to be equivalent on all symptom clusters. This actually suggests that exposure therapy and cognitive therapy may actually be working through the same mechanism. Now, you can't actually prove that to be true, because doing so is predicated on accetpting the null hypothesis. But it certainly is a possiblity to be considered. Regarding the speed with which anxiety drops in EMDR sessions, compard to to exposure therapy, it is interesting to note that within-session fear reduction although sometimes associated with better outcome exposure therapy, seems to be less consistently a predictor of outcome than fear-activation and between-session fear reduction. While the observation you make may suggest the operation of a different mechanism, it still falls short of what would be considered very strong evicence: a double dissociation. Double dissociations occur in two flavors. Flavor one is the cross-over interaction, such that the same manipulation has opposite effects on two different treatemtns. So, it would be strong evidence for the operation of different mechanisms if, say, promoting emotional engagement enhanced exposure therapy but reduced the effectiveness of EMDR. The second flavor is a pair of single dissociations. In this case we identify one variable that effects EMDR but not exposure therapy, and a second variable that effects exposure therapy but not EMDR. Now, I actually can consider the possibility that eye movements may have an effect on in-session anxiety. My best guess at this point is that it serves as a mild distractor that reduces the emotional impact of the fear image. I develope this idea to some extent in my comments on the studies by Adnrade/Kavanagh et al., and Sharpley et al. Whether this distraction effect is best characterized as "titrating" exposure (implying that you are slowing helping people confront the feared image, sort of like using a higherarchy) or encouraging some kind of avoidance is yet to be determined. I'm open to both possibilities.
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