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Contemp Clin Trials. 2009 Jan;30(1):13-9. doi: 10.1016/j.cct.2008.08.001. Epub 2008 Aug 12.

Telephone-based assessments to minimize missing data in longitudinal depression trials: a project IMPACTS study report.

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University of Texas Southwestern Medical Center, Dallas, Texas 75390-9119, USA.



Missing data in clinical efficacy and effectiveness trials continue to be a major threat to the validity of study findings. The purpose of this report is to describe methods developed to ensure completion of outcome assessments with public mental health sector subjects participating in a longitudinal, repeated measures study for the treatment of major depressive disorder. We developed longitudinal assessment procedures that included telephone-based clinician interviews in order to minimize missing data commonly encountered with face-to-face assessment procedures.


A pre-planned, multi-step strategy was developed to ensure completeness of data collection. The procedure included obtaining multiple pieces of patient contact information at baseline, careful education of both staff and patients concerning the purpose of assessments, establishing good patient rapport, and finally being flexible and persistent with phone appointments to ensure the completion of telephone-based follow-up assessments. A well-developed administrative and organizational structure was also put in place prior to study implementation.


The assessment completion rate for the primary outcome for 310 of 504 subjects who enrolled and completed 52 weeks (at the time of manuscript) of telephone-based follow-up assessments was 96.8%.


By utilizing telephone-based follow-up procedures and adapting our easy-to-use pre-defined multi-step approach, researchers can maximize patient data retention in longitudinal studies.

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