I certify that I have read this study and that in my 

 opinion it conforms to acceptable standards of scholarly 

 presentation and is fully adequate, in scope and quality, as 

 a dissertation for the degree of Doctor of Philosophy. 



Frank G. Martin 

 Professor of Statistics 



This dissertation was submitted to the Graduate Faculty 

 of the College of Agriculture and to the Graduate School and 

 was accepted as partial fulfillment of the requirements for 

 the degree of Doctor of Philosophy. A . 



April 1994 ^^ &_ 



Dean, College of 

 Agriculture 



Dean, Graduate School 



