Levitt, Malta, Martin, Davis, and Cloitre (2007) evaluated the effectiveness of cognitive behavioral therapy (CBT) for treating PTSD and related symptoms for survivors of the 9/11 terrorist attacks on the World Trade Center (WTC). They used a pretest-posttest design to see if CBT was successful at reducing the symptoms of PTSD and related symptoms of depression. They used the Modified PTSD Symptom Scale Self-Report (MPSS-SR) questionnaire to measure symptoms of PTSD and the Beck Depression Inventory (BDI) self-report questionnaire to measure symptoms of depression. For both questionnaires, lower scores indicated fewer symptoms. The authors reported the following results:
Pre- to post treatment t tests for the WTC sample revealed significant decreases in scores on the MPSS-SR, [t(37) = 12.74, p < .01]; as well as on the BDI [t(34) = 7.36, p < .01]. (Levitt et al., 2007, p. 1427)
(a) Was this a repeated-measures design or a matched-pairs design?
(b) Which questionnaire (MPSS-SR or BDI) was completed by more participants?
(c) Did the authors find support for their hypothesis? Explain.