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Revised 1/4(80 <br />r <br />Section 816.116 (a) Continued. <br />llhere: xl = the average cover or production for the undisturbed <br />range site. <br />x2 = the average cover or production for [he reference <br />area. <br />nl = sample size from undisturbed range site. <br />n2 = sample size from the reference area. <br />SP = the pooled variance of samples from both locations <br />expressed as: <br />S2 = £ xl + ~x2 <br />P <br />nl+n2 - 2 <br />Field sampling will meet the following standards. Where shrubs <br />and trees dominate at least 30 percent of the total plant cover <br />for the range site, the sample size will attain a statistical <br />minimum of 80% confidence level with 20% precision. Range sites <br />with less than 30 percent of the cover made up of trees and shrubs <br />will ^eet a statistical minimum of 90% confidence with 10% precision. <br />Adequacy of sample size will be determined using the following <br />formula (USDI, Bureau of Land Management Manual 4412-Physical <br />Resource Studies, August 10, 1979): <br />2 <br />N = t s <br />m <br />p x <br />Where: N = Minimum number of transects necessary to sample <br />m within the prescribed precision and confidence; <br />t = A value from the "t" distributicn table which <br />establishes the level of confidence; t = 1.282 for <br />80% confidence, t = 1.645 for 90% confidence; <br />5 = Standard deviation calculated as: <br />S = £Cx-3c)2 <br />n-1 <br />Where: x = transect mean <br />x = mean of transect means <br />n = number of transects <br />816-157 QJ j <br />