A class of saturated row–column designs

A new class of row–column designs is proposed. These designs are saturated in terms of eliminating two-way heterogeneity with an additive model. The (m,s)-criterion is used to select optimal designs. It turns out that all (m,s)-optimal designs are binary. Square (m,s)-optimal designs are constructed and they are treatment-connected. Thus, all treatment contrasts are estimable regardless of the row and column effects.     

Minimal augmented square designs and their extensions

Minimal square designs are proposed and compared. All treatment contrasts in both designs are estimable under the existence of two-way heterogeneity. That is, all designs are treatment-connected. Extended treatment-connected designs are generated by adding one column to minimal treatment-connected square designs. The extended designs not only have lower variances in paired comparisons of unreplicated treatments but also provide necessary degrees of freedom to estimate the process error. (M,S)-optimal extended designs are constructed systematically. Both square designs and their extensions have large numbers of unreplicated treatments.     

Posttraumatic stress disorder (PTSD) symptoms among firefighters: Roles of resilience and locus of control

Firefighting is a an extremely stressful occupation that risks exposure to traumatic events as part of the job. Despite this, the literature on stress and trauma pays little attention to this occupation and its generalization to other, high risk occupations. This study examined resilience and work locus of control as predictors of posttraumatic stress disorder (PTSD) symptoms among Nigerian firefighters. Participants were 116 paid, professional firefighters (98 males and 18 females) who completed the Post-Traumatic Stress Disorder Checklist-Civilian Version (PCL-C), Resilience Scale (RS-14), and Work Locus of Control Scale (WLCS) and provided vital demographic information. Multiple regression analysis was used to analyze the data. Results showed that resilience negatively predicted PTSD symptoms such that higher resilience was associated with fewer symptoms of PTSD. Work locus of control was a positive predictor of PTSD symptoms, indicating that externality of control beliefs in the workplace was associated with more PTSD symptoms. Relevant demographic factors especially higher years of service, being a senior firefighter, and higher educational status were associated with lower PTSD symptoms. Findings underscore the potential value of resilience training and implementing behavioral health programs to modify firefighters’ external locus of control beliefs. Interventions should consider resilience and locus of control focused interventions as protective factors for PTSD.