Re: differential mechanism/dose reponse

Again, my aplogies for being a bit on edge. On to your comments.

You ask some very good questions to for which I don't have a good answer. I'm not sure why you observed the pattern that you did, but it is an interesting one. Just so that readers of this exchange can follow us, I've taken the liberty of duplicating some information from your Table 1.

For Treatment SUDS
EMDR at Pretreatment: 7.4 (0.9)
EMDR at Posttreatment: 0.4 (1.0)

Exposure at Pretreatment: 7.2 (2.6)
Exposure at Posttreatment: 8.3 (2.0)

There was a significant decrease in the Treatement SUDs for the EMDR group, but no change for exposure therapy.

For Assessment SUDs
EMDR at Pretreatment: 5.8 (1.6)
EMDR at Posttreatment: 5.0 (1.3)

Exposure at Pretreatment: 8.2 (3.1)
Exposure at Posttreatment: 8.5 (1.8)

No change from pre-to-posttreatment for either group.

I don't know why EMDR showed a decrease in SUDs for the Treatment SUDs, while exposure therapy did not. I also don't know why the change in SUDs that was observed in the EMDR group during Treatment disappeared during Assessment. However, I'm also not convinced that this difference in patterns is terribly important with respect to outcome. To wit:

1. Groups did not differ on standardized outcome measures.

2. No evidence was presented that changes in SUDs during EMDR treatment was associated with outcome.

Therefore, I'm not convinced that the difference in patterns reflects the operation of different mechanisms of recovery. At the present, the pattern seems more incidental than anything. Recall that Pitman et al. (1996) found that classic Foa & Kozac indicators of emotional processing that have been found to be modestly predictive of treatment outcome for exposure therapy were also modestly predictive of treatment outcome in EMDR.

The idea behind your study was innovative. IMO, however, it fell short in design in a couple of important ways that limit the kinds of conclusions that can be drawn. It would be very informative if you study were replicated with the following changes:

1. Have both therapists deliver both treatments to eliminate the confounding of treatment effects with therapist effects.

2. Provide a full course of therapy in which sessions are continued until a specific criterion is achieved (e.g., 70% reduction on IES total scores, or some other measure of PTSD) or an upper limit on the number of sessions (e.g., 15) has been reached. Conduct good assessments of process and outcome measures at each session.

3. Expand the range of outcome measures (e.g., include measures of depression and general anxiety, changes in social functioning)

4. Conduct analyses to determine whether there are differences between the therapies in patterns of process variables, and then conduct analyses to determine if these patterns predict outcome.

(I know the advice was unsolicited, but I couldn't restrain myself.)

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