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• Cuantitatlve Comparability of 1990 and 1992 Areas <br />Cover data from the 1990 and 1992 Yoast sampling efforts were used to assess the <br />statistical 'comparability' of data sets from the same vegetation types in the two years and <br />areas. Mean 'first hit' cover values and standard deviations were used in the formula <br />present in Colorado Mined Land Reclamation Division Vegetation Guideline, page 16: <br />I xj - xil <br />tc = <br />~ --- 2 -- 2 ---- <br />+~ <br />nj ni <br />where: <br />tc = calculated t value <br />xj =Reference area cover sample mean <br />xi =Affected vegetation type sample mean <br />nj =Number of reference area samples <br />ni =Number of affected vegetation type samples <br />sp2 =pooled sample variance cak:ulated as follows: <br />• (nj - 1) (sj2) + (ni-1) (sit) <br />(nj + ni) -2 <br />The calculated t value is compared to a t value taken from a table of two-tailed values at (nj <br />+ ni) - 2 degrees of freedom and 95% confidence. If the calculated t value is less than the <br />table t-value, the null hypothesis (ie. that there is no difference between the populations) <br />is accepted and 'comparability' is indicated. <br />Results of calculations for the 1990 Yoast Baseline and 1992 Supplemental Areas were as <br />follows: <br />ASS en <br />tc = 2.026 tt , 2.048 <br />Since tt > tc, the null hypothesis is accepted and comparability is indicated. <br />Mountain Brush <br />• tc = 0.739 tt = 2.048 <br />Since 1<> Tc, the null hypothesis is accepted and comparability is indicated. <br />31 <br />