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• where d = 0.1 (to estimate within 10% of the population <br />mean value) <br />s = standard deviation of the data set <br />n = number of measurements in the data set <br />z = mean of the data set <br />0.84 = t-value with infinite degrees of freedom for a one- <br />tailed test with p = 0.2 <br />The following table lists x, s, n, nmin' and t for each data set <br />within each sample area. The nmin value should be comparable to <br />or less than the n value, however, these estimates are conserva- <br />tive based on the factor of 2 in the equation. The t-values should <br />exceed the critical value of 0.84, to indicate statistical confidence <br />• of at least 80%. Some of xhe-nmin values are higher than the n values, <br />most are comparable or lower. Nearly all the t-values exceed 0.84. <br />Thus, sampling is generally adequate within the confidence levels des- <br />cribed. <br /> <br />