EMDR FORUM ARCHIVE, 2000
Re:Scientific Jargon vs. reality
Cahill · 12/31/02 at 2:44 PM ET
Ricky: I'm neither Larry nor Lawrence. Rather, it's Shawn. I'm not nearly as well published as Larry Cahill of Cahill & McGaugh fame (among others). In follow-up to discussion of the Davidson & Parker meta-analysis, your post of 12/28 stated " This meta-analysis is controversial for a number of reasons, this opinion being one of them. If you look at the actual studies pertaining to the possible role of eye movements, you would almost certainly come to a different conclusion than the authors of this meta-analysis." I then pointed out, and you agreed 12/29 post, that one cannot criticize a study or meta-analysis on the basis of its conclusions. Indeed, you state " I agree with you that studies should be judged according to their design/procedures, not their results. Like any other study, judgment calls are inherent to meta-analyses. How to select studies for inclusion, whether/how to weight them, how to interpret/categorize their findings." But then, you don't specify what problems of sampling, weighting, interpretation, etc. you find in the Davidson & Parker meta-analysis. I trust that this is simply because you don't have access to the paper at this time and that, in the future, you will in fact provide us with a critique of the Davidson & Parker paper that explains why we should question their conclusion regarding the role of eye movements. Just so that we are clear, the following quotes indicate just exactly what Davidson & Parkder did conclude regarding eye movements (emphasis mine): "Is eye movement--or indeed, any alternating movement--a necessary component of EMDR? The near-zero effect sizes indicate that eye movement is unnecessary...The effect sizes for the outcome measures are small, and ***we have no evidence that eye movements or other alternating stimuli are necessary.***" Now, just to be clear, these authors are using between-group effect sizes, comparing EMDR with eye movements to some kind on EMDR minus eye movements condition. It is important to understand this, otherwise one might mistakenly think they are saying EMDR with eye movements is not effective. Quite emphatically, they conclude that EMDR works, but that the incremental effects of eye movements per se are small and that there is "no evidence that eye movements or other alternating stimuli are necessary." Transitioning now to your argument for the role of eye movements in the efficacy of EMDR, it has two components, a positive and a negative component. The positive component is that there are "findings suggestive of such effect in many studies" but you don't provide specific citations. I trust that you will do so when you get your office in order. The negative component of your argument is that "there is certainly no definitive proof to the contrary either." Of course there is no "definitive proof" that eye movements do not contribute to outcome. The reason is that it is logically impossible to prove a negative. The burden of proof ALWAYS rests with those making a positive assertion. And thus far, you have failed to meet this burden. Moreover, the argument about low power in small n studies is somewhat misleading. The power of a study is not only determined by sample size, but also the magnitude of the experimental effect. If one is studying a powerful manipulation, then even studies with small sample sizes can have sufficient power. Thus, the question that has to be answered is "How large an effect should be expected?" Unfortunately, Shapiro has changed her mind about this. If you go back to her original 1989 paper, she was quite emphatic that eye movements were the most important ingredient of EMDR, and, IMHO, it is a perfectly legitimate reading of Shapiro 1989 that one would expect a LARGE effect size when comparing EMDR with and without eye movements. Empirically, the effect sizes are NOT large. Indeed, Davidson & Parker found the average effect size to be "near zero." Now, it is true that Shapiro has since changed her mind, and now suggests that it is not necessarily eye movements but perhaps any form of laterally alternating stimuli or dual stimulation. Moreover, because saccades (which are quite different from the smooth eye tracking movements induced through tracking a moving finger or light bar) occur even when you tell people to fix their eyes in one place, people have made the (absurd IMHO) argument that a "no eye movement" condition is actually "an eye movement condition." Plus, EMDR is supposedly so chock full of other effective elements (none of which have been shown to add to treatment outcome) that EMDR minus eye movements is still a powerful intervention, except, of course, when you apply it to veterans. In other words, eye movements are now expected to have a small effect size, thus requiring large samples. And, to top it off, all of this movement on Shapiro's part is supposedly based on clinical experience that preceded the various dismantling studies, so that she can deflect criticism by claiming that the researchers responsible for these weren't adequately testing her most recent hypotheses. Now, if it is true that we can rely on clinical experience to shape and alter EMDR so drastically, then why do we do research? If your conclusion about the role of eye movements in EMDR is limited to "we don't know whether eye movements affect outcome" then you and I are in very close agreement and we both are in close agreement with Davidson and Parker, who concluded "we have no evidence that eye movements or other alternating stimuli are necessary." Note, they didn't say nor have I ever said "We have proven that eye movements don't add to outcome." Yet, again your post from 12/28 states that someone actually reviewing the relevant studies "would almost certainly come to a different conclusion than the authors of this meta-analysis." What would that different conclusion be? I wish to further point out that if we were to adopt your two pronged approach that (1) there is at least some evidence in favor of the hypothesis under consideration and (2) no definitive proof that the hypothesis is not true as the basis for drawing scientific conclusions, then we would have to give scientific credence to the possibility that some people have actually been kidnapped by aliens from outerspace. Why? Because there is SOME evidence that it has happened (i.e., testimony from those who ostensibly been abducted) AND there is no definitive evidence that people have not been kidnapped by aliens. Ergo, since we can't be certain that such abductions don't happen we should treat this as a reasonable hypothesis. How absurd! We absolutely should NOT give any scientific credence to the possibility that people are being kidnapped until proponents of this idea can provide adequate evidence for their claims. Finally, regarding you comment that you teach exposure more often than you teach EMDR, I have to admit, I have no idea what that has to bear on the topic of whether eye movements add anything to outcome in EMDR. For those of you who managed to stick through this long post, Happy New Year!
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