II. FOEIv'IDLA FOR GOLIPUTING THE STAimRD DEVIATION 2/ 



S ^ . \ 



n — I 



where s s. standard deviation of the sample of tree volumes 

 y = volume of a single tree 

 Z: =. "the sum of" 



n number of individual tree voluraes in the sample 

 III. FORMULA FOR COia'UTING COEFFICIENT OF VARIATION 



cv = 



y 



where CV = coefficient of variation 

 s = standard deviation 

 y = mean volume of sample 

 IV. FORMULA FOR COlIPUTniJ SAMPLE SIZE 



P% icvr 



where n = number of trees needed in the sample 



t = number of standard units chosen in the 

 probability limits 



CV = coefficient of variation 



E =. accuracy desired, expressed as a certain 

 percentage of the mean 



N = nuinber of trees in the sale 



If a probability of 58 percent is considered sufficient (as has been 

 used throughout this report) then t = 1 and the formula becomes: 



t + N 



(This foimula is the basis for data in Figure 1.) 



2^7 For more details in the m.ethod of calculating this and other 

 statistics, see 3chum.aker and Chapman (11_) or other texts on 

 statistical methodSo 



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