?Soil Testing A researcher took water samples from a stream running through a forest and groundwater in the forest. The samples were collected over the

Chapter 13, Problem 3

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Soil Testing A researcher took water samples from a stream running through a forest and groundwater in the forest. The samples were collected over the course of a year. Each sample was analyzed for the concentration of dissolved organic carbon (mg/L) in it and categorized according to the type of water collected. Water was collected from streams (surface water), groundwater was collected from organic soil, and groundwater was collected from mineral soil. The researcher wanted to determine if the mean concentration of dissolved organic carbon was the same for each collection area. The results are presented in the following table.

(a) What is the response variable in this study?

(b) What is the factor? How many levels of treatment does the factor have?

(c) State the null and alternative hypotheses.

(d) A normal probability plot of each sample (organic, mineral, and surface) indicates the data come from a normally distributed population. Use the following summary statistics from StatCrunch to verify the equal population standard deviation requirement.

(e) Use the following StatCrunch output to test if the means are the same at the a = 0.01 level of significance.

(f) Interpret the P-value.

(g) Shown are side-by-side boxplots of each type of collection area drawn in StatCrunch. Do the boxplots support the analytic results? Which collection area type appears to differ from the rest?

(h) The following display represents the results of Tukey’s test obtained from StatCrunch. Which pairwise means differ?