Missing Data in Longitudinal Trials – Part B, Analytic Issues

By Juned Siddique, DrPH; C. Hendricks Brown, PhD; Donald Hedeker, PhD; Naihua Duan, PhD; Robert D. Gibbons, PhD; Jeanne Miranda, PhD; Philip W. Lavori, PhD

Longitudinal designs in psychiatric research have many benefits, including the ability to measure the course of a disease over time. However, measuring participants repeatedly over time also leads to repeated opportunities for missing data, either through failure to answer certain items, missed assessments, or permanent withdrawal from the study. To avoid bias and loss of information, one should take missing values into account in the analysis. Several popular ways that are now being used to handle missing data, such as the last observation carried forward (LOCF), often lead to incorrect analyses. We discuss a number of these popular but unprincipled methods and describe modern approaches to classifying and analyzing data with missing values. We illustrate these approaches using data from the WECare study, a longitudinal randomized treatment study of low income women with depression.

ABOUT THE AUTHORS

Juned Siddique, DrPH, is with the Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago. C. Hendricks Brown, PhD, is with Prevention Science and Methodology Group, Department of Epidemiology and Biostatistics, College of Public Health, University of Illinois at Chicago. Donald Hedeker, PhD, is with Division of Biostatistics, University of Illinois at Chicago. Naihua Duan, PhD, is Professor of Biostatistics in Psychiatry, Departments of Biostatistics and Psychiatry, Columbia University; and Director, Division of Biostatistics, N.Y. State Psychiatric Institute, New York, N.Y. Robert D. Gibbons, PhD, is with Professor of Biostatistics and Psychiatry, and Director of the Center for Health Statistics, University of Illinois at Chicago. Jeanne Miranda, PhD, is with UCLA Health Services Research Center. Philip W. Lavori, PhD, is Professor of Biostatistics, and Chair, Department of Health Research and Policy, Stanford University School of Medicine.

Address correspondence: Juned Siddique, DrPH, Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, 680 N. Lake Shore Drive, Suite 1102, Chicago, IL 60611; fax: 312-908-9588; e-mail: siddique@northwestern.edu.

Dr. Siddique, Dr. Brown, Dr. Hedeker, Dr. Duan, Dr. Gibbons, Dr. Miranda, and Dr. Lavori have disclosed no relevant financial relationships.

EDUCATIONAL OBJECTIVES

1. Describe design and analytic methods for dealing with missing data in longitudinal studies.
2. Discuss which methods should be used and which methods should not be used for analysis of longitudinal studies with missing data.
3. Describe the various types of missing data and how they can be dealt with analytically.