Structural Models of Comorbid Anxiety and Depression in a Primary-Care Older Adult Sample: Effect of Medical Illness Severity, Threat, Chronicity, and Progressiveness on Model Fit

Recent research suggests that anxiety disorders may be more common in later life than previously thought. Among other factors, the presence of comorbid mood disorders and medical illness confounds accurate assessment and diagnosis of these conditions in the elderly. There have been few studies, however, examining the structural relationships between anxiety and depression with older-adult samples, and even fewer have considered the effect of medical illness on these relationships. This study examined three established structural models of anxiety and depression, using a clinical sample of older adults seeking treatment in a primary-care setting (N = 2,163). It was hypothesized that the presence of comorbid medical illness would act as a moderating variable in evaluating the fitness of these models. Results indicated that a hierarchical model represented the most parsimonious fit to the full sample. Tests of factorial invariance revealed variance in model fit as a function of illness severity and threat, and as a function of illness chronicity and progressiveness. Specifically, the relationship of somatic symptoms to anxiety varied by combined severity/threat, as well as by chronicity/progressiveness. These findings support previous conceptualizations of the relationship between anxiety and depression. Implications of these results for taxonomy, assessment, and intervention are discussed. Palmer, William Michael, 2007, UMSL p. 3 Acknowledgements This research was funded in part by a Dissertation Fellowship awarded July 1. 2006 by the Graduate School, University of Missouri-St. Louis. The database upon which this study was based was originally developed as part of the Primary Care Research in Substance Abuse and Mental Health for the Elderly (PRISME), a study funded jointly by the U.S. Substance Use and Mental Health Services Administration (SAMHSA), U.S. Department of Veterans’ Affairs, U.S. Health Resources Services Administration, and the Centers for Medicare and Medicaid Services. I would particularly like to acknowledge the efforts of Cynthia Zubritsky. Ph.D., Betsy McDonel-Herr, Ph.D., Sue Levkoff, Ph.D., and Marian Mullaly, in facilitating access to the PRISM-E database for use in this study. This study would not have been possible without the input and contributions of each of the members of the dissertation committee. I would like to extend my sincere appreciation to Bob Calsyn, Ph.D., for his numerous curbside consultations and willingness to share his wisdom; to Kami White, Ph.D., for her expertise and invaluable suggestions throughout the development of this study; to Dr. Zubritsky for her assistance in navigating the PRISM-E dataset; and to Bobbie Lee, Dr. P.H. , for her unique contributions to elucidating the medical-illness variables that were essential in the development of the research questions. Palmer, William Michael, 2007, UMSL p. 4 To my advisor, mentor, and friend, Dr. Ann Steffen—I offer my humble gratitude for every opportunity extended, every idea generated, every door opened, and the countless times that you went far above and beyond the call of your profession to facilitate my growth as a scholar, practitioner, and person. In the interest of owning my successes, I will grudgingly concede that I may indeed have achieved all that I have without your support, guidance, and direction. But in my heart of hearts, I cannot begin to imagine how. To all my classmates, professors, and the administrative staff who have shared their friendship, knowledge, and experience; who listened to me postulate, overreach, and whine; and who helped me navigate the minefields of college life—thank you for sharing this ride with me. I couldn’t have asked for finer colleagues, teachers, supporters, and friends, and I hope that I have given back to each of you at least a measure of what you have given me. To my wife, Dorothy; my children, Mary, Darrell, Chris, Brad, Sara, and Ryan—thank you for your love, your patience, your support, understanding, and sacrifice in the service of my achievements. You truly are the reason that I persevere, my inspiration and motivation. This work is dedicated to the memory of my mother, Alice Jean Palmer (1942-2003), who was the first person to look at me and see a doctor. Palmer, William Michael, 2007, UMSL p. 5 Table of