Am J Psychiatry ; Under the intent-to-treat principle, these noncompliant participants will be counted in their original treatment groups. Although there were complete sample size formulas available for cluster randomization, a much simpler method can be used if the intraclass correlation coefficient of the outcome data can be reasonably assumed [28]. Thus, the main analysis is a cross-sectional comparison of results at a fixed point in time rather than a longitudinal profile comparison. Additional visits were allowed when clinically indicated, as were additional inpatient or outpatient treatment for clinical emergencies. The randomizations were done for each participant using permuted blocks of four in three blocks of CAPS severity scores to ensure the balance of treatment groups by CAPS score. A difference of 0.

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Participants n 5 at ten sites were randomly assigned to receive one of the two treatments: There were minor logistic challenges as well, such as finding a time when officecetner group members could attend a session when individuals would not know their group assignment until after randomization. The Long Journey Home: The effectiveness of psychotherapy. The independent raters also made global ratings of adherence and competence and rated specific elements to provide a manipulation check, e.

The sample size officecebter is based on univariate analysis using comparisons at specific time points at each site.

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Researchers who employ group interventions need to consider the possible inflation of sample size requirements due to the correlation of outcomes within therapy groups. This tends to reduce the apparent effect size and thus lowers the power to detect a true effect size of 0. However, we rejected this approach because of a concern that having therapists deliver both treatments would make it hard for them to offivecenter the treatments distinct in application.


Another part of the planning process was to examine program evaluation data on the nature of treatment being delivered in the VA.

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On the one hand, it was important that the total number of sessions be realistic and comparable in both conditions. With a large sample, the inclusion of even one questionnaire measured at pretreat- ment, posttreatment, and follow-up can create many total hours of work for study personnel and participants officecentsr. Analysis by intention-to-treat implies complete follow-up of outcomes in participants, and this in turn requires their cooperation with measurement.

Fontana A, Rosenheck R. With a sample size ofthe study was the largest randomized trial ever conducted of psychotherapy for PTSD and is one of the largest studies ifficecenter group therapy for any disorder.

Am J Psychiatry ; Reliability, validity, and diagnostic utility. Inflation of Variance Suppose ngroup 5 mk participants are assigned to k groups, m per group, then a direct calculation yields: The study provides an example of how to address the unique challenges posed by multisite trials of group psychotherapy through attention to meth- odological and statistical issues.

Controlled Clinical Trials Given the size of CSPmeasures were chosen based on their quality and the extent to which they were judged to be essential for broadly representing likely outcomes.


Instead, to ensure that therapist effects were balanced across treatments, we randomized therapists to the single treat- ment each was to deliver. Health status, somatization, and severity of posttraumatic stress disorder in Vietnam combat veterans with posttraumatic stress disorder.

However, the most significant challenges came from the effects of group clustering on sample size estimation and data analysis. Am J Psychia- try ; This article describes the ofricecenter and methods of the study. Received February 11, ; accepted September 18, A group-based design officrcenter as this delays treatment for enrolled participants who must wait while a cohort is being assembled.

Comparison of three models of treatment.

The randomizations were done for each participant using permuted blocks of four in three blocks of CAPS severity scores to ensure the balance of treatment groups by CAPS score. The pivotal comparison was at the end of treatment. During the second phase of screening, the interviewer reviewed an informed consent form with potential participants to explain the study in more detail.

Statistical Issues The outcome of treatment was measured at several points in time for each individual.

The former project manager is Beth H.

Data collection was completed in June In such cases, the change was documented for use in data analysis.