Evaluation of Septic Tank and Subsurface Wetland for
Evaluation of Septic Tank and Subsurface Wetland for
Evaluation of Septic Tank and Subsurface Wetland for
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Confidence Interval Sample Calculation:<br />
Determine 90% confidence interval <strong>for</strong> RT3 Total Nitrogen<br />
X Z<br />
σ<br />
n<br />
± ( α /2)<br />
For 90% α = 1-0.9 = 0.1<br />
Using the t-Table<br />
α /2 = 0.05 (this is called p <strong>for</strong> the table so p = 0.05)<br />
degrees <strong>of</strong> freedom (df) = sample size – 1, or n – 1 df = 7-1 = 6<br />
= 7.8 ± (1.9432)<br />
7.094<br />
7<br />
= 7.8 5.2 ±<br />
There is 90% confidence that the mean is between 2.6 <strong>and</strong> 13.0.<br />
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