Bisson and Andrew(2007) conducted a meta-analysis of cognitive behavior therapy (CBT) as a treatment for posttraumatic stress disorder (PTSD). They found 14 studies for which they had clinicians’ ratings of PTSD symptoms in both a CBT-focused condition and a wait list/usual care condition. The results are presented here.

Apply a meta-analysis to these data and draw the appropriate conclusions.

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CBT Control Study N Mean St. Dev. N Mean St. Dev. Kubanyl Foal 44 45 15.80 14.40 40 40 71.90 23.80 45 12.60 8.37 15 26.93 8.47 Kubany2 18 10.10 19.30 14 76.10 25.20 Resick 81 23.00 19.92 40 69.73 19.19 Cloitre 22 31.00 25.20 24 62.00 22.70 Foa2 10 15.40 11.09 10 19.50 7.18 Keane 11 28.80 10.05 13 31.90 31.90 Ehlers 14 21.58 28.56 14 74.55 19.12 Vaughan 13 23.00 10.20 Brom 27 56.20 24.10 23 Blanchard 27 23.70 26.20 24 Fecteau 10 37.50 30.40 Gersons 22 3.00 10.00 Rothbaum 20 21.25 22.50 122222 17 28.50 8.90 66.40 24.30 54.00 25.90 10 74.60 24.70 20 9.00 13.00 20 64.55 19.87