IRCT20251009067560N1 IRCT 2025-11-23 University of social welfare and rehabilitation sciences Effectiveness of Cognitive Processing Therapy in Post-Traumatic Stress Disorder and Investigating the Mechanism of Symptom Change During Treatment Using Idiographic Network Analysis: A Clinical Trial Effectiveness of Cognitive Processing Therapy in Post-Traumatic Stress Disorder and Investigating the Mechanism of Symptom Change During Treatment Using Idiographic Network Analysis: A Clinical Trial 2025-12-22 anticipated 45 Complete https://irct.ir/trial/87586 interventional Randomization: Randomized, Blinding: Single blinded, Placebo: Not used, Assignment: Parallel, Purpose: Treatment, Randomization description: Randomization Method For participant allocation to study groups, block randomization will be used to maintain balance in the number of individuals between experimental and control groups throughout the sampling process. Block randomization is particularly important in studies with relatively small sample sizes, such as the present study, to prevent the accumulation of participants in one group and to ensure that baseline characteristics of participants remain balanced across groups. Method Details Block Size: Given the allocation ratio of 2:1 (experimental group: 30 participants, control group: 15 participants), blocks will consist of three participants, such that in each block, two participants will be assigned to the experimental group and one to the control group. Generation of Random Sequence: For each block, the order of participant allocation will be determined randomly. For example, in a three-participant block, possible sequences could be: Experimental–Control–Experimental Control–Experimental–Experimental Experimental–Experimental–Control The selection of each block’s sequence will be performed using software such as R or Excel. Implementation of Randomization: After generating the block sequences, each participant will be assigned to a group according to the order of entry into the study and the predetermined random sequence. This ensures that the number of participants in each group always remains consistent with the specified ratio and that baseline characteristics are balanced. Blinding and Coding: To maintain study impartiality, the randomization sequence will be prepared by an independent researcher, and group codes will be sealed in opaque envelopes or stored in an encrypted electronic system. This ensures that team members administering the intervention remain unaware of group assignments. Advantage of This Method: Block randomization ensures that throughout the study, groups are nearly equal in size and in important baseline variables, thereby reducing error due to unbalanced allocation, Blinding description: Due to the nature of the intervention, complete blinding of participants and intervention providers is not feasible. However, to reduce bias, full blinding of the outcome assessor and the statistical analyst will be implemented. Specifically: The researcher responsible for recruiting participants will become aware of group allocation only after confirming each participant's eligibility, using a sealed envelope or centralized electronic system. Other research team members will not have access to the allocation sequence. The assessor of primary and secondary outcomes (the individual conducting measurements and data collection) will be blinded to participant groupings and will work exclusively using anonymous codes (ID) at all stages. The statistical analyst will receive the dataset only after coding. The analyst will remain blinded to group allocation until the completion of the final analysis. In case of any adverse event or clinical necessity, unblinding will only be permitted with committee approval and proper documentation of the reason. To ensure the integrity of this process, at the end of the study the outcome assessor and the analyst will be asked the standard “guess the group” question to evaluate the success of the blinding. 1 Post-traumatic stress disorder. Intervention group: Receive 12 sessions of cognitive processing therapy. No - There is not a plan to make this available Justification or reason for not sharing IPD is No further information available.