With reference to Example 20, Chapter 7, construct a 95% confidence interval for the true standard deviation of the lead content.

Data From Example 20

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EXAMPLE 20 At test of a normal population mean Scientists need to be able to detect small amounts of contaminants in the environ- ment. As a check on current capabilities, measurements of lead content(g/L) are taken from twelve water specimens spiked with a known concentration. (courtesy of Paul Berthouex). 2.4 2.9 2.7 2.6 2.9 2.0 2.8 2.2 2.4 2.4 2.0 2.5 Test the null hypothesis = at the 0.025 level of significance. 2.25 against the alternative hypothesis > 2.25 There are no outliers or other indications of non-normality. As a preliminary step we calculate x = 2.483 and s = 0.3129.