Chapter 11: Problem 4
Basic Definitions Define the terms given. Factor
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Chapter 11: Problem 4
Basic Definitions Define the terms given. Factor
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Identify the treatments or factors and levels. A supervisor would like to compare the effect of using raw material obtained from four different sources, each processed using three fixed temperature settings.
What are the assumptions needed for the results of Tukey's test to be valid?
Water samples were taken at four different locations in a river to determine whether the quantity of dissolved oxygen, a measure of water pollution, varied from one location to another. Locations 1 and 2 were selected above an industrial plant, one near the shore and the other in midstream; location 3 was adjacent to the industrial water discharge for the plant; and location 4 was slightly downriver in midstream. Five water specimens were randomly selected at each location, but one specimen, corresponding to location \(4,\) was lost in the laboratory. The data and a MS Excel analysis of variance computer printout are provided here (the greater the pollution, the lower the dissolved oxygen readings). $$ \begin{array}{clcccc} \hline \text { Location } & {\text { Mean Dissolved Oxygen Content }} \\ \hline 1 & 5.9 & 6.1 & 6.3 & 6.1 & 6.0 \\ 2 & 6.3 & 6.6 & 6.4 & 6.4 & 6.5 \\ 3 & 4.8 & 4.3 & 5.0 & 4.7 & 5.1 \\ 4 & 6.0 & 6.2 & 6.1 & 5.8 & \\ \hline \end{array} $$ $$ \begin{aligned} &\text { SUMMARY }\\\ &\begin{array}{lrrrr} \hline \text { Groups } & \text { Count } & \text { Sum } & \text { Average } & \text { Variance } \\ \hline 1 & 5 & 30.4 & 6.08 & 0.022 \\ 2 & 5 & 32.2 & 6.44 & 0.013 \\ 3 & 5 & 23.9 & 4.78 & 0.097 \\ 4 & 4 & 24.1 & 6.025 & 0.0292 \\ \hline \end{array} \end{aligned} $$ $$ \begin{aligned} &\text { ANOVA }\\\ &\begin{array}{lcrcccc} \hline \text { Source of Variation } & \text { SS } & \text { df } & \text { MS } & \text { F } & \text { P-value Fcrit } \\ \hline \text { Between Groups } & 7.8361 & 3 & 2.6120 & 63.656 & 9 \mathrm{E}-09 & 3.287 \\ \text { Within Groups } & 0.6155 & 15 & 0.0410 & & & \\ \text { Total } & 8.4516 & 18 & & & & \\ & & & & & & \\ \hline \end{array} \end{aligned} $$ a. Do the data provide sufficient evidence to indicate a difference in the mean dissolved oxygen contents for the four locations? b. Compare the mean dissolved oxygen content in midstream above the plant with the mean content adjacent to the plant (location 2 versus location 3 ). Use a \(95 \%\) confidence interval.
What are the assumptions regarding the sampled populations and the sampling methods in order to use an analysis of variance?
A study was conducted to compare automobile gasoline mileage for three formulations of gasoline. Four automobiles, all of the same make and model, were used, and each formulation was tested in each automobile, thus eliminating automobile-to-automobile variability. The data (in miles per gallon) follow. $$ \begin{array}{ccccc} \hline & & {\text { Automobile }} \\ \hline \text { Formulation } & 1 & 2 & 3 & 4 \\ \hline \mathrm{A} & 25.7 & 27.0 & 27.3 & 26.1 \\ \mathrm{~B} & 27.2 & 28.1 & 27.9 & 27.7 \\ \mathrm{C} & 26.1 & 27.5 & 26.8 & 27.8 \\ \hline \end{array} $$ a. Do the data provide sufficient evidence to indicate a difference in mean mileage per gallon for the three gasoline formulations? b. Is there evidence of a difference in mean mileage for the four automobiles? c. Suppose that prior to looking at the data, you had decided to compare the mean mileage per gallon for formulations \(\mathrm{A}\) and \(\mathrm{B}\). Find a \(90 \%\) confidence interval for this difference. d. Use an appropriate method to identify the pairwise differences, if any, in the average mileages for the three formulations.
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