Alumni (Fellow)

Bobby Moulder

John S. Lillard Jefferson Fellow
Jacksonville, Florida
B.S. University of North Florida (2014)
Ph.D. University of Virginia (2020)
Graduate School of Arts & Sciences


Bobby Moulder is a Ph.D. recipient in quantitative psychology in the Department of Psychology at the University of Virginia. He is a member of The International Max Planck Research School on the Life Course (LIFE), guest researcher of human dynamics and healthy aging at the University of Zurich, and consultant for the World Health Organization’s healthy aging initiative. Bobby received his B.S. in psychology with minors in both mathematical science and statistics from the University of North Florida. His current research involves the intersection of multivariate statistics, nonlinear dynamics, chaos theory, and human behavior. Along with fellow students, Bobby revived the Jefferson Journal of Science and Culture, acting as co-cheif editor of the 2019 edition.

Thesis Description:

Latent Multivariate Maximal Lyapunov Exponents
Sensitive dependence on initial conditions is a defining quality of chaotic systems in which small differences in how two units begin may lead to large differences in these units later in time. This property has strong theoretical implications for interpretability and predictability of time based phenomena. However estimation of maximal Lyapunov exponents, a defining metric of sensitive dependence on initial condition, from data with measurement error is difficult. This impedes the study of sensitive dependence in psychological and behavior research as these areas of research tend to have relatively high levels of measurement error compared to other fields of study. This is unfortunate as many psychological phenomenon such as life satisfaction, drug use behaviors, and genetic differences in behavior are considered to display sensitive dependence on initial condition. Many Psychological researchers use structural equation modeling (SEM) to account for measurement error when modeling behavioral data. SEM is a versatile method for modeling systems of linear equations capable of explicitly modeling measurement error. This dissertation seeks to use SEM as a means of estimating maximal Lyapunov exponents from data with measurement error. This estimated maximal Lyapunov exponent via SEM will be termed a Latent Lyapunov Exponent (LLE). First, a mathematical derivation of an SEM equivalent of the R-method for estimating maximal Lyapunov exponents is shown. Then a series of simulation studies compare the proposed method to currently established methods on bias, variance, and MSE. A separate simulation will then test the efficacy of the LLE method for a smaller number of samples. Extensions of LLE to multivariate space will then be discussed. Next, a real data example from socially anxious individuals over a number of weeks will serve as an illustration of the use of the LLE method. Finally, limitations, and future directions will be discussed.

DOI:10.18130/v3-6f76-0y53 LINK: https://libraetd.lib.virginia.edu/public_view/41687j13h

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