V 



Probability of a Tree Being Unsound in Cubic Foot Volume — Unforked and Forked Trees 



The model form for the probability of a tree being unsound in cubic -^oor volume to 

 be applied to both total stem and merchantable predictions is 



-X 



PrC^ = 1.0/(1.0 + e ^) 



where 



PrC^-= Predicted probability of. a tree being unsound in cubic foot volume 



X = A function of the tree's measured attributes. 



a 



Weighted, nonlinear regression procedures (Hamilton 1974) were used to determine 

 the equations for X^. The resulting equations, along with the number of trees used, are 



presented in table 11. An F-statistic was used to test the significance of the models. 

 The equation for blackjack pine on the Lincoln National Forest was significant at the 

 95 percent level, and all other equations were significant at the 99 percent level. 

 Methodological details can be found in appendix X. 



16 



