Table 5 . --Statistics for log of basal area growth equations 



Equation Number of RMqnR r2 Modified Modified 



type observations KMbC^K K rmsqR r2 



Blackjack pine 

 with even-aged 

 data 



33,155 



0.8001 



0.2000 



0.5155 



0.4839 



Blackjack pine 

 without even-aged 

 data 



27,268 



.8223 



.1779 



.5425 



.4576 



Yellow pine 



4,558 



.9334 



.0678 



.8847 



.1165 



Because of the presence of within diameter class variation, the statistics quantifying the 

 fit of the equations are unduly pessimistic. The equations explain between class variation 

 and, therefore, the statistics were modified by eliminating the within diameter class variation 

 component to better reflect the true fit of the equations. These "modified" statistics are 

 also found in table 3. 



The results show that the blackjack pine equations developed with the even- and uneven- 

 aged data explained over 48 percent of the between diameter class variation, the other black- 

 jack pine equation explained over 45 percent, and the yellow pine equation explained only 

 about 12 percent. For the blackjack pine, however, the equations do better at predicting 

 managed growth than virgin growth. I obtained the statistics in table 4 by computing the 

 residuals of each indicated data set around the final models. These statistics show that the 

 blackjack pine equation developed with the even- and uneven-aged data, explained only about 19 

 percent of the virgin uneven-aged variation, but it explained over 63 percent and almost 78 

 percent of the variation for the managed uneven- and even-aged data sets, respectively. The 

 other blackjack pine equations explained a little over 19 percent of the virgin and almost 64 

 percent of the managed uneven-aged variation. Because the managed stand is of primary concern, 

 these results are important. 



Table ^.--Modified coefficients of determination for various data sets by equation type 



Modified 



Equation Virgin Managed Managed 



type uneven-aged uneven-aged even-aged 



data data data 



Blackjack pine 



with even-aged data 0.1941 0.6334 0.7780 



Blackjack pine 



without even-aged data .1922 .6364 



Yellow pine .0440 .0873 



8 



