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A random sample of soil specimens was obtained, and the amount of organic matter (%) in the soil was determined for each specimen, resulting in the accompanying data (from 鈥淓ngineering Properties of Soil,鈥 Soil Science, 1998: 93鈥102).

\(\begin{array}{l}1.10 5.09 0.97 1.59 4.60 0.32 0.55 1.45\\0.14 4.47 1.20 3.50 5.02 4.67 5.22 2.69\\3.98 3.17 3.03 2.21 0.69 4.47 3.31 1.17\\0.76 1.17 1.57 2.62 1.66 2.05\end{array}\)

The values of the sample mean, sample standard deviation, and (estimated) standard error of the mean are \(2.481,1.616,\) and \(.295,\) respectively. Does this data suggest that the true average percentage of organic matter in such soil is something other than \(3\% \)? Carry out a test of the appropriate hypotheses at significance level \(.10\). Would your conclusion be different if a \(\alpha = .05\) had been used? (Note: A normal probability plot of the data shows an acceptable pattern in light of the reasonably large sample size.)

Short Answer

Expert verified

The true average percentage is something other than \(3\% \) is not supported by appropriate evidence at both significance level.

Step by step solution

01

Define p-value in hypothesis testing.

The null hypothesis states that the population mean is equal to the value mentioned in the claim. If the null hypothesis is the claim, then the alternative hypothesis states the opposite of the null hypothesis.

\(\begin{array}{l}{H_0}:\mu = 0\\{H_a}:\mu \ne 0\end{array}\)

The formula for the value of the test statistic is given by, \(t = \frac{{\bar x - {\mu _0}}}{{s/\sqrt n }}\).

02

Test the appropriate hypothesis.

The mean is the ration of sum of all values and the total number of values.

\(\begin{aligned}{c}\bar x &= \frac{{1.1 + 5.09 + 0.97 + ... + 2.62 + 1.66 + 2.05}}{{30}}\\ &= \frac{{74.44}}{{30}}\\ &\approx 2.4813\end{aligned}\)

The square of the variance is the standard deviation.

\(\begin{aligned} s &= \sqrt {\frac{{{{(1.1 - 2.4813)}^2} + \ldots . + {{(2.05 - 2.4813)}^2}}}{{30 - 1}}} \\ &\approx 1.6156\end{aligned}\)

Let the given be:

\(\begin{array}{l}n = 30\\\alpha = 0.10/0.05\end{array}\)

Claim that the true average percentage is something other than\(3\% \).

The value of the test statistic:

\(\begin{aligned}{c}t &= \frac{{\bar x - {\mu _0}}}{{s/\sqrt n }}\\ &= \frac{{2.4813 - 3}}{{1.6156/\sqrt {30} }}\\ &\approx - 1.759\end{aligned}\)

The P-value is the chance of getting the test statistic's result, or a number that is more severe. The P-value is the number (or interval) in the column header of the T table in the appendix that contains the t-value in the row \(\begin{aligned}{c}df &= n - 1\\ &= 30 - 1\\ &= 29\end{aligned}\) for the student.

\(0.05 = 2 \times 0.05 < P < 2 \times 0.10 = 0.20\)

As the P-value is smaller than the significance level, so the null hypothesis is rejected.

\(\begin{array}{l}P > 0.10 \Rightarrow Fail to Reject {H_0}\\P > 0.05 \Rightarrow Fail to Reject {H_0}\end{array}\)

The true average percentage is something other than \(3\% \) is not supported by appropriate evidence at both significance level.

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