American Statistical Association
New York City
Metropolitan Area Chapter

New York State Psychiatric Institute
at Columbia University Medical Center
Biostatistics Seminar



Eva Petkova, Ph.D.
Associate Professor of Child and Adolescent Psychiatry
Director, Biostatistics Division
New York University Child Study Center


Measures of biological phenomena, in general, and of psychiatric conditions, in particular, often exhibit symmetric shapes resembling a normal distribution. However, it is well known that members of homogeneous populations with symmetric unimodal distributions can exhibit very distinct characteristics. In medical research, an important goal is to identify groups of subjects characterized by a particular trait or quality and to distinguish them from other subjects in a clinically relevant way.

Statistical approaches predominantly used for that purpose have been based on the assumption of underlying categories, whether observed or latent, such as latent class or mixture and growth mixture models. In this talk, I will present an approach to characterizing heterogeneity, which is based on principal points methodology, that does not presuppose the existence of distinct categories. The approach can be used with any multivariate distribution, but in this talk, I will present the case of functional (longitudinal) data modeled with mixed effects models.

As an illustration, the following clinical question will be addressed: After a depressed subject is treated with an antidepressant and responds to the acute treatment, can we tell whether s/he still needs the drug to maintain response? Data from two discontinuation depression studies will be used. The studies were designed and carried out by investigators from DES at NYSPI and Columbia U.

This is a joint work with T. Tarpey.

Biographical Note

Eva Petkova received her Ph.D. in Physics at the Sofia University in Bulgaria. She then obtained a second Ph.D. in Statistics from Pennsylvania State University. Dr. Petkova is the Director of the Division of Biostatistics at the NYU Child Study Center. Her primary interest is the development and application of statistical methods for psychiatric research. Her technical expertise is in statistical modeling and design of clinical experiments, which includes regression methods for clustered longitudinal, categorical and survival data, finite mixture modeling, causal inference and models for missing data. Dr. Petkova also has extensive experience in designing, monitoring, and analyzing data from large single-site and multi-site psychiatric clinical trials in the areas of treatment and services research.

Date: Tuesday, November 17, 2009
Time: 3:00 - 4:00 P.M.
Location: New York State Psychiatric Institute
1051 Riverside Drive
6th Floor Multipurpose Room (6602)
New York, New York


Coffee: 2:45 to 3:00 P.M.
Reception: 4:00 to 4:30 P.M.

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