Department of Statistics Seminar
North Carolina State University

presents

Dr. Shyamal Peddada

National Institute of Environmental Health Sciences (NIEHS)

"A General Methodology for Testing Order Restrictions with Applications to Toxicology"

ABSTRACT

In many applications, researchers are often interested in testing for order restrictions on various parameters of interest. For example, using the rodent assays, researchers at the National Toxicology Program (NTP) are interested in detecting dose related trends in tumor response to a given chemical. There are several test procedures available in the literature to perform tests for order restrictions. In addition to being computationally intensive, some of these procedures can be either too liberal or too conservative (Piegorsch, 1990). An example is the likelihood ratio test. On the other hand there are procedures which are computationally simple but make assumptions which are often not true or hard to verify. An example of such a procedure is the Cochran-Armitage trend test for detecting binomial trends.
In this talk we introduce a computationally simple test procedure which can be applied to a very broad collection of testing problems. Simulation studies reveal that the proposed test performs very well compared to some of the popular alternative tests. Our procedure is based on a general estimation procedure recently introduced in Hwang and Peddada (1994). Unlike the restricted maximum likelihood estimators (RMLE), these point estimators are simple to compute for any arbitrary order restriction, even when the data are correlated. For certain types of order restrictions, it is well known that the RMLE can perform very poorly relative to the unrestricted maximum likelihood estimator (UMLE). On the contrary the new point estimator universally dominates the UMLE. Test procedures described in this talk are illustrated by applying to an NTP rodent tumor data.

Friday, September, 14, 2001*

3:35 - 4:35 pm

206 Cox Hall

Refreshments will be served on the second floor of Dabney Hall (left of Room 222) at 3:00 pm.
*Special informal lunchtime seminar/discussion. 12:15-1:15, 208 Patterson.