Browsing by Author "Cavell Brownie, Committee Co-Chair"

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Age-Dependent Tag Return Models for Estimating Fishing Mortality, Natural Mortality and Selectivity
(2005-09-09) Jiang, Honghua; Kenneth Pollock, Committee Chair; Cavell Brownie, Committee Co-Chair; David Dickey, Committee Member; Joseph Hightower, Committee Member
We extend the instantaneous rates formulation of fisheries tag return models to allow for age-dependence of fishing mortality rates in Chapter 1. This is important in many applications where tagged fish vary over a large range of ages (and sizes). We focus on a model based on assuming selectivity by age is constant over years and that above a certain age selectivity is fixed at 1. We show that it is possible to allow natural mortality, M, to vary by age and year. We allow for incomplete mixing of tagged fish and for fisheries to be pulse, continuous or continuous over part of the year. We focus on the case where all or most age classes are tagged each year. We investigate model identifiability and how well parameters can be estimated using analytic and simulation methods. Results show that some models with the tag reporting rate estimated are singular or near-singular. The age-length key method commonly used for age specification may produce substantial errors in converting size to age, especially for the older fish. To reduce such errors, in Chapter 2 we propose two alternative sampling designs to the standard one of tagging all age classes: one where only age 1 fish are tagged, another where both age 1 and age 2 fish are tagged. Catch-and-release fisheries have become very important to the management of overexploited recreational fish stocks. Tag return studies where the tag is removed regardless of fish disposition have been used to assess the effectiveness of restoration efforts for these catch-and-release fisheries. In Chapter 3, we extend the instantaneous rate formulation of tag return models introduced in Chapter 1 to catch-and-release tagging studies. We illustrate the methods using multiple age class tag return data on striped bass (Morone saxatilis) from the Maryland Department of Natural Resources (MDNR). We found evidence that M is age dependent and that M has increased since 1999 possibly due to an outbreak of the disease (mycobacteriosis) in striped bass in the Chesapeake Bay.
Anisotropic Diffusion in Fluorescence Microscopy
(2004-04-08) Wan, Xiaohai; Sharon R. Lubkin, Committee Chair; Cavell Brownie, Committee Co-Chair; Zhilin Li, Committee Member
Diffusion of tracer molecules in configurations of collagen fibrils may be used to determine anisotropy of fiber distributions in fluorescence microscopy experiments. Mathematical simulations are used to study the feasibility of these kinds of experiments. The anisotropic diffusion phenomenon can be modeled as a random walk process in simulated completely aligned fibers using the Monte Carlo method. We studied the relationships between the diffusion coefficients (either parallel or perpendicular to fiber orientation) and two influencing factors (density of fibers and relative size of fibers and tracer molecules). Using simulations and statistical analysis, we found that for a given fiber density, relatively bigger size tracer molecules are preferred in order to detect certain level of anisotropy of the fibers. If tracer molecules are too small compared with fibers, even high density of fibers can help little to detect any anisotropy.
New Methods using Levene Type Tests for Hypotheses about Dispersion Differences
(2006-10-25) Liu, Xiaoni; David Dickey, Committee Member; Jason Osborne, Committee Member; Cavell Brownie, Committee Co-Chair; Dennis Boos, Committee Chair
Testing equality of scale arises in many research areas including clinical data analysis. In contrast to procedures for tests on means, tests for variances derived assuming normality of the parent populations are highly non-robust to non-normality. Levene type tests are well known to be robust tests for equality of scale for the one-way design; the current standard test uses the ANOVA F test on absolute deviations from the sample medians. We first develop a new modified version of the standard Levene test that improves its null performance and power. Applying the Box-Anderson correction to the ANOVA F test further improves the performance. We also extend the robust Levene type tests to the two-way design with one observation per cell, the randomized complete block design (RCB). Currently, the available Levene type tests for RCB designs employ either standard ANOVA F tests on the absolute values of ordinary least squares (OLS) residuals, or weighted least squares (WLS) ANOVA F tests on the OLS residuals. These two tests can be liberal, especially under non-normal distributions. Instead, we use OLS ANOVA F tests on the absolute values of residuals obtained from models fit by least absolute deviation (LAD) estimation and by Huber Proposal 2 M-estimation. We also apply bootstrap methods to these Levene type tests and compare by simulation these Levene type tests in terms of robustness and power.