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f <br />S TnTE OP COI ORnr)O ni~'nnnn u. i• r~^v,~~,r.., <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, Executive Director <br />M1NEU LAND NECLA1~lA'I'ION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-35fi7 <br />David C. Shelton <br />Director <br />MEMORANDUM <br />T0: Sue Mowry <br />FROM: M. S. Savage SAVA!-E <br />RE: H-G Statistical Analysis C- ~ 0 3- ~~ <br />DATE: February 11, 1981 <br />Formula n = 2 S2 Z2 <br />min <br />(dX)2 <br />This formula is appropriate however: <br />999 <br />1. 1.28 as a value for Z is not appropriate for a 90% level. They should <br />be using t = 1.645 (two tailed test at 90% confidenc0). However, this <br />is the correct value for an 80% confidence two-tailed test which they <br />should be using. <br />2. 0.2 is not the degree of confidence, it is the level of accuracy <br />desired and should be 0.1 in this instance, since they wish to <br />estimate within 10% of the actual mean. <br />3. The formula for this case should be: <br />n = 2(5)2(1.28)2 <br />min <br />(0.1)2(X)2 <br />4. If H-G is utilizing this formula to determine minimum sample size <br />for reference areas and premining areas they must address where the <br />value for S (standard deviation) comes from. In order to accurately <br />apply this formula, the value for S must be a pooled variance (standard <br />deviation) of the nature: <br />S2 = (nX 1)5X1 + (nY-1)gYl <br />nX + nY - 2 <br />where: <br />nX - number of samples from premining area <br />,~ <br />