Each study in the PTSD-Repository was coded for risk of bias (ROB) in specific domains as well as an overall risk of bias for the study. Detailed information about the specific coding strategy is available in Comparative Effectiveness Review [CER] No. 207, Psychological and Pharmacological Treatments for Adults with Posttraumatic Stress Disorder. (See our "Risk of Bias" data story.) Most domains were rated as Yes (i.e., minimal risk of bias), No (i.e., high risk of bias) or Unclear (i.e., bias could not be determined). The overall study rating is based on the domains and is coded as low, medium or high risk of bias. The 4 domains that were included as components of the overall rating include: Selection bias--randomization adequate, allocation concealment adequate, groups similar at baseline and whether they used intention to treat analyses; Performance bias--care providers masked and patients masked; Detection bias--outcome assessors masked; Attrition bias--overall attrition less than or equal to 20% vs over 20%; differential attrition less than or equal to 15% vs over 15%. Additional items assessed (but not considered as part of the overall rating) include: Reporting bias--all prespecified outcomes reported; Reporting bias--method for handling dropouts; Outcome measures equal valid and reliable; Study reports adequate treatment fidelity based on measurements by independent raters.