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adequate sample, n m i n , has been collected in accordance with the Cochran formula (below) for <br />determining sample adequacy, whereby the population is estimated to within 10% of the true mean (p) <br />with 90% confidence. <br />When the inequality (n min <_ n) is true, sampling is deemed adequate; and n min is determined as <br />follows: <br />nmin = (t 2 2) I (0.1 X )2 <br />where: n = the number of actual samples collected (initial size = 50 or 20) <br />t = the value from the one - tailed t distribution for 90% confidence with n -1 <br />degrees of freedom; <br />s 2 = the variance of the estimate as calculated from the initial samples; <br />T = the mean of the estimate as calculated from the initial samples. <br />If the initial samples do not provide a suitable estimate of the mean (i.e., the inequality is false), <br />additional samples would be collected until the inequality (n min <_ n) becomes true. <br />2.4 Success Evaluation <br />Success evaluations involve a direct comparison (and where necessary statistical testing) of the <br />ground cover parameter. In the case of ground cover, comparisons are made against reference area <br />data of the same year. There are two methods in which reference area comparisons can be made. The <br />first is a perennial cover comparison in which annual and biennial cover is completely deleted from <br />vegetation cover values. Implementation of this method requires noxious weeds and annual and biennial <br />cover to be removed from the total Phase II cover data set as well as the two reference areas. Perennial <br />cover is the remaining data classification and can be used in a direct or statistical reference area <br />comparison. <br />The second method uses guidance provided by CDRMS. The rules and regulations provide an <br />opportunity for an allowable contribution of 10% relative cover of annuals and biennials to be used in a <br />reference area comparison. Using this comparison method, annual and biennial cover should also be <br />used on the reference area when comparisons are made. Implementation of this method requires <br />CEDAR CREEK ASSOCIATES, Inc. Page 7 Colowyo Coal Company <br />2008 Phase II Evaluation (Updated Dec -10) <br />