The area and volume statistics of the re survey are based on the 

 initial cover-type area, modified by sample line transects and 

 volume sample plots shown in the following table: 



Area 



Volume 



County 



Number of 

 line transects 1/ 



Number of plots 2/ 



Spokane 

 Stevens 

 Lincoln 

 Whitman 



Ferry 



Pend Oreille 



128 

 76 

 75 



151 

 19 

 2 



339 

 220 



163 

 469 

 44 

 3 



1/ 



Transects for the six counties totaled 15,745 chains, 

 196.8 miles, or approximately 35 chains per location. 



Based on an analysis of variance each plot was considered 

 0.6 of an independent observation. 



2/ 



ACCURACY OF THE DATA 



In determining the extent of various cover types and stand-condition 

 classes, there are two possible sources of error: (l) errors in 

 classifying the cover of the field samples and in compiling the field 

 data, and (2) sampling errors. The former result from mistakes of 

 judgment or technic and the complexity of. the cover which not infre- 

 quently grades from one class into another with no clearly defined 

 boundaries. These errors were minimized by the exercise of care and 

 skill, but it is seldom possible to evaluate them. An effort was 

 made to maintain a high order of accuracy and uniformity of standards 

 in the classification, collection, and compilation of sample data, by 

 field checks, by a continuing program of training, and by cross 

 checks in the office. 



Sampling errors, as measured by the standard error of estimate, on the 

 other hand do not involve human errors but rather are theoretical 

 measures of the reliability of estimates based on the variability ex- 

 hibited by sample measurements. They generally vary inversely with 

 the square root of the number of observations and directly with the 

 square root of the unsampled proportion of the total population. 

 Hence, they can be controlled by altering either the number of samples, 

 the size of individual samples, or both. 



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