The article examined was conducted by Ulmer, Edinger, & Calhoun (2011), to explore the feasibility of cognitive behavioral therapy (CBT) and sleep interventions for veterans who are diagnosed with PTSD and insomnia. The experimental design, randomly assigned veterans to a treatment or control group (Ulmer et al., 2011). Ulmer et al. (2011) hypothesized CBT for insomnia and imaginal rehearsal therapy (IRT) for nightmares would improve sleep quality significantly.
The Data Analysis
In order to test the hypothesis, Ulmer et al. (2011) used a linear mixed effects model to determine the mean values. This means there are both fixed and random effects determining the mean values through a longitudinal analysis (Ulmer et al., 2011).