Introduction: Experimental designs are represented as the gold standard for assessing the effectiveness of interventions. Yet despite the strengths of these designs intervention studies often fail to find statistically significant differences between comparison treatments. What might we learn about differential treatment effects if a qualitative component were added?

Purpose: To illustrate how quantitative and qualitative methods can be incorporated into an intervention research design to provide greater depth of information about treatment effects.

Methods: A mixed methods approach was utilized to examine the effectiveness of Eye Movement Desensitization and Reprocessing (EMDR) in reducing trauma symptoms in adult female survivors of childhood sexual abuse. The sample consisted of 59 women who were randomly assigned to either EMDR, eclectic therapy or a delayed treatment control group for six 90-minute individual therapy sessions. Standardized measures of depression, anxiety, PTSD symptoms and negative self beliefs were used to assess pre and post treatment trauma symptoms. After completion of post-testing those survivors who had received either EMDR or eclectic therapy were individually interviewed to gather qualitative data about their perceptions of the effectiveness of the treatment they received. The interviews were tape recorded and consisted of 14 open-ended questions. A structured five stage qualitative data analysis process was employed and quantitative data was used to triangulate the qualitative findings.

Results: The quantitative results indicated that the experimental treatment (EMDR) was effective in comparison to the control group, but it did not demonstrate superiority over the comparison treatment (eclectic therapy). The qualitative data revealed substantial distinctions in the importance and effect of the client-therapist relationship and in the depth of change reportedly caused by the two different therapies.

Implications: A mixed methods approach to intervention research produces better, more accurate findings than either approach can provide individually. It enhances the ability to identify therapeutic outcomes of interest and to capture additional indicators of treatment effectiveness.