232 



TIMBER TRENDS IN THE UNITED STATES 



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.01 .02 .03 04.05.06 .08.10 .15 .20 25.30 40.50.60 .80 1.00 

 PROPORTION OF AREA OR VOLUME IN BREAKDOWN 



The sampling error (in terms of one standard deviation) 

 for the total area of commercial forest land in the United 

 States at the time of field surveys was 0.1 percent (2.5 

 percent per million acres). Sampling errors for inventory 

 volume at the time of field surveys was calculated at 0.3 

 percent for the United States as a whole (8.5 percent per 

 billion cubic feet). Sampling errors for breakdowns of 

 forest area, as by stocking classes of forest types, for 

 example, may be approximated from relationships shown 

 in the following figure which includes the ratio of the 



standard error of an area or volume breakdown to the 

 percentage error of the estimate of total area or volume: 

 In using this chart (1) determine the total area and the 

 sampling error for a given State (e.g., 26.3 million acres 

 in Georgia with an error plus or minus 0.3 percent), (2) 

 determine the percent of the total made up by the item 

 in question (e.g., 10 percent in sawtimber stands), (3) 

 determine the multiplying factor from the above figure 

 (e.g., a factor of 3 for 10 percent of area), and (4) multiply 

 the sampling error by the multiplying factor (e.g., 3X0,3 

 percent = 0.9 percent). 



