Indicator how often the subject has difficulty concentrating as part of PTSD Checklist Stressor (PCLS).
Weathers, F., Litz, B., Herman, D., Huska, J., & Keane, T. (October 1993). The PTSD Checklist (PCL): Reliability, Validity, and Diagnostic Utility. Paper presented at the Annual Convention of the International Society for Traumatic Stress Studies, San Antonio, TX. Public domain available from: www.ncptsd.va.gov/ncmain/ncdocs/assmnts/ptsd_checklist_pcl.html