| Testing for Spatial Correlation in Nonstationary Binary Data with application to Aberrant Crypt Foci in Colon Carcinogenesis |
| In an experiment to understand colon carcinogenesis, all animals were exposed to a carcinogen while half the animals were also exposed to radiation. Spatially, we measured the existence of what are referred to as aberrant crypt foci (ACF), namely morphologically changed colonic crypts that are known to be precursors of colon cancer development. The biological question of interest is whether the locations of these ACFs are spatially correlated: if so, this indicates that damage to the colon due to carcinogens and radiation is localized. Statistically, the data take the form of binary outcomes (corresponding to the existence of an ACF) on a regular grid. We develop score--type methods based upon the Matern and conditionally autoregression (CAR) correlation models to test for the spatial correlation in such data, while allowing for nonstationarity. Because of a technical peculiarity of the score--type test, we also develop robust versions of the method. The methods are compared to a generalization of Moran's test for continuous outcomes, and are shown via simulation to have the potential for increased power. When applied to our data, the methods indicate the existence of spatial correlation, and hence indicate localization of damage. |
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Tanya Apanasovich Texas A&M University Student Poster Session |
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April 4-5, 2003
Texas A&M University
College Station, TX
Email:
cots@stat.tamu.edu
Fax: (979) 845-3144
Phone: (979) 845-3141