Analysis of sample variations of the 451 line transects indicate that 

 the standard errors of estimate for the six^ counties combined are 

 ±1.3 percent for total forest land area, ±1.4 percent for commercial 

 forest land area and ±19.5 percent for noncommercial forest land area, 

 Accordingly, the probabilities are 2 out 3 that actual forest land, 

 commercial forest land and noncommercial forest land areas are, 

 respectively, within ±51,000 acres, ±52,000 acres, and ±43,000 acres 

 of the areas given in this report if measurements and computing 

 errors introduced no bias. 



In determining timber volumes, the possible sources of error include 

 in addition to those cited above (3) inaccurate measurement of sample 

 plots, tree diameters, tree heights, and cull, and (4) bias resulting 

 from improper construction, selection, and use of tree-volume tables. 

 All reasonable effort was made to eliminate errors from these sources. 

 Analysis of the variation of the 1238 one-fifth-acre volume plots 

 indicate that the standard errors of the volume sample are: saw-timber 

 and pole trees ±4.0 percent, saw-timber trees ±5.4 percent, and pole 

 trees ±5.9 percent. The standard errors of total cubic volume are: 





i 



Percent 



Million 





a 

 ■ 



: cubic feet 



Saw-timber 



and pole trees ; 



±4.2 



: ±177 



Saw- timber 



trees ; 



±5.6 



: ±151 



Pole trees 





±6.0 



: ± 88 



Stand volume was originally computed in cubic feet and converted to 

 board feet by use of board-foot/cubic-foot ratios correlated with 

 tree size. These ratios should have small errors. Therefore, 

 standard error of board-foot volume is judged to be the same as the 

 error of cubic-foot volume for saw-timber trees only, or +5.6 per- 

 cent. In terms of board-foot volume of all species for the block as 

 a whole this is equivalent to a sampling error of ±834 million feet. 



The statistics on cutting drain are based in part on a 100-percent 

 canvass of producers and in part on sampling data. Only 20 percent 

 of the cubic-foot and 15 percent of the board-foot cutting drain are 

 based on samples. An indeterminable error, however, is introduced 

 in translating production into drain. The statistics for the sum of 

 all drain items for the block as a whole are judged to be within ±10 

 percent, i.e. within ±2,800 M cubic feet and +15,000 M board feet. 



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