Abstract #300627

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JSM 2003 Abstract #300627
Activity Number: 86
Type: Contributed
Date/Time: Monday, August 4, 2003 : 8:30 AM to 10:20 AM
Sponsor: Section on Physical and Engineering Sciences
Abstract - #300627
Title: Estimating the Width of the Junction between a Low Plane and a High Mesa
Author(s): Robert S. Wilson*+ and Stuart A. Gansky
Companies: University of California and University of California, San Francisco
Address: PO Box 170657, San Francisco, CA, 94117-0657,
Keywords: change point ; segmented regression ; proc model ; dentinoenamel junction
Abstract:

Picture to the left a low plane, and to the right a high mesa, each with relatively mild changes in elevation. In between is the junction, a jumble of rocks forming a ramp from plane to mesa top. The task is to estimate the width of this junction. Our method assumes the reality to be three straight lines, the plane, the junction, and the mesa, with abrupt changes (change points) to and from the junction. Vertical measurements contain error about these lines. Horizontal measurements have negligible error. We estimate the horizontal values of the two change points and from their difference, the width of the junction. We use available software, SAS proc model. One task is to maximize the ability of proc model to provide estimates low in bias and variance. A second task is to assess the stability of the settings used by proc model when presented with multiple datasets differing in width and slope of the junction, and in magnitude of errors. Using simulated data, we discuss optimum settings and the stability of these settings. We acknowledge support from DHHS/NIH/NIDCR R01DE13029 and P60DE13058.

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