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A study to assess the capability of subsurface flow wetland systems to remove biochemical oxygen demand (BOD) and various other chemical constituents resulted in the accompanying data on \(x=\) BOD mass loading \((\mathrm{kg} / \mathrm{ha} / \mathrm{d})\) and \(y=\) BOD mass removal \((\mathrm{kg} / \mathrm{ha} / \mathrm{d})\) ("Subsurface Flow Wetlands-A Performance Evaluation," Water Envir: Res., 1995: 244–247). $$ \begin{array}{c|cccccccccccccc} x & 3 & 8 & 10 & 11 & 13 & 16 & 27 & 30 & 35 & 37 & 38 & 44 & 103 & 142 \\ \hline y & 4 & 7 & 8 & 8 & 10 & 11 & 16 & 26 & 21 & 9 & 31 & 30 & 75 & 90 \end{array} $$ a. Construct boxplots of both mass loading and mass removal, and comment on any interesting features. b. Construct a scatter plot of the data, and comment on any interesting features.

Short Answer

Expert verified
Mass loading shows skewness and outliers; scatter plot suggests a moderate positive relationship with mass removal.

Step by step solution

01

Draw Boxplot for BOD Mass Loading (x)

To draw a boxplot for the BOD Mass Loading data, first calculate the five-number summary: minimum, first quartile (Q1), median (Q2), third quartile (Q3), and maximum.\For the data\( x = [3, 8, 10, 11, 13, 16, 27, 30, 35, 37, 38, 44, 103, 142] \):\- **Minimum**: \(3\)\- **Q1**: Median of \(3-13\) (first half), which is \(10\)\- **Median (Q2)**: Middle value, which is \((27+30)/2 = 28.5\)\- **Q3**: Median of \(27-44\) (second half), which is \(37\)\- **Maximum**: \(142\)\Plot these as a boxplot, identifying the range, interquartile range, and checking for outliers such as \(142\), which is notably higher.
02

Draw Boxplot for BOD Mass Removal (y)

For the BOD Mass Removal, calculate the five-number summary similarly:\For the data \( y = [4, 7, 8, 8, 10, 11, 16, 26, 21, 9, 31, 30, 75, 90] \):\- **Minimum**: \(4\)\- **Q1**: Median of \(4-10\) (first half), which is \(8\)\- **Median (Q2)**: Middle value, \((16+26)/2 = 21\)\- **Q3**: Median of \(21-31\), which is \(30\)\- **Maximum**: \(90\)\Draw the boxplot for this data, note that 90 could indicate an outlier.
03

Analyze Boxplots

After drawing the boxplots for both data sets, observe and comment:- **BOD Mass Loading (x)**: Outliers like \(142\) suggest high variability with a skewed distribution.\- **BOD Mass Removal (y)**: An outlier at \(90\) also suggests skewness.\Both distributions show potential skewness and outliers, indicating variability in efficiency or differences in wetland conditions.
04

Construct Scatterplot

To create a scatter plot, graph the pairs of data points \((x, y)\) from the given table. Plot these points on a coordinate grid, with BOD Mass Loading \(x\) on the horizontal axis and BOD Mass Removal \(y\) on the vertical axis.
05

Analyze Scatterplot

Examine the scatter plot for patterns or trends. Look for: - **Linear Relationships**: Whether increases in mass loading correlate to increases in mass removal.\- **Clusters or Outliers**: Check for outliers such as \((142, 90)\), indicating inconsistencies in data.\The scatter plot might show a moderate positive relationship, given increases in\(x\) can lead to increases in \(y\), with a couple of outlying values.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Boxplot
A boxplot, also known as a whisker plot, is an effective graphical representation to visualize the distribution of a dataset. It highlights several important statistics that provide a clear overview of the dataset's spread and central tendency. This includes:

  • Minimum
  • First Quartile ( Q1 )
  • Median (Second Quartile, Q2 )
  • Third Quartile ( Q3 )
  • Maximum

The boxplot essentially splits the data into quartiles, with the box representing the interquartile range (IQR), which encompasses 50% of the data. The lines extending from the top and bottom of the box, often referred to as "whiskers," indicate the range of the data, excluding any outliers. Outliers are typically plotted as individual points outside the whiskers and represent data points that deviate significantly from the rest of the dataset.

By constructing boxplots for the BOD Mass Loading and Removal data, we can quickly identify outliers such as 142 in the loading data and 90 in the removal data. These extreme values suggest variability and skewness in the distributions, offering insights into potential variations in the performance of the wetland systems.
Scatter Plot
A scatter plot is a type of graph that uses Cartesian coordinates to display values for two variables for a set of data. Each point on the graph corresponds to an (x, y) pair from the dataset, making it an essential tool for understanding relationships between variables.

When constructing the scatter plot for BOD Mass Loading vs. Mass Removal, place Mass Loading ( x ) on the horizontal axis and Mass Removal ( y ) on the vertical axis. This allows us to observe any potential correlations.

  • Look for **linear patterns or trends**, indicating whether an increase in one variable tends to lead to an increase in the other (positive correlation), or a decrease (negative correlation).
  • Identify **clusters or outliers** that might indicate anomalies or specific regions where data points behave differently, such as the point (142, 90) in this dataset.

The scatter plot often reveals a general trend or pattern, as seen in this dataset, where there seems to be a moderately positive relationship between Mass Loading and Removal. Such visual insights are invaluable for further analyses or hypothesis formulation regarding the efficiency and behavior of wetland systems.
Five-number summary
The five-number summary is a simple yet powerful way to summarize a dataset with just five key statistics:

  • The **Minimum** value
  • The **First Quartile (Q1)**, which separates the lowest 25% of the data
  • The **Median (Second Quartile, Q2)**, the middle value that divides the dataset into two equal halves
  • The **Third Quartile (Q3)**, which separates the lowest 75% of the data
  • The **Maximum** value

These statistics give a comprehensive view of the data’s distribution, spread, and center. For the BOD Mass Loading dataset, the five-number summary is 3, 10, 28.5, 37, 142. The summary reveals that most values are clustered between 10 and 37, with a high outlier at 142.

Similarly, for the BOD Mass Removal dataset, the summary includes 4, 8, 21, 30, and 90. Here, the data shows a more moderate spread, but still includes an outlier at 90. Computing the five-number summary is foundational for making boxplots and understanding the underlying characteristics of the datasets, providing a snapshot of the overall distribution and highlighting any potential outliers or anomalies.

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Most popular questions from this chapter

"Mode-mixity" refers to how much of crack propagation is attributable to the three conventional fracture modes of opening, sliding, and tearing. For plane problems, only the first two modes are present, and the mode-mixity angle is a measure of the extent to which propagation is due to sliding as opposed to opening. The article "Increasing Allowable Flight Loads by Improved Structural Modeling" (AIAA J., 2006: 376-381) gives the following data on \(x=\) mode- mixity angle (degrees) and \(y=\) fracture toughness \((\mathrm{N} / \mathrm{m})\) for sandwich panels use in aircraft construction. $$ \begin{array}{l|llllllll} x & 16.52 & 17.53 & 18.05 & 18.50 & 22.39 & 23.89 & 25.50 & 24.89 \\ \hline y & 609.4 & 443.1 & 577.9 & 628.7 & 565.7 & 711.0 & 863.4 & 956.2 \\ x & 23.48 & 24.98 & 25.55 & 25.90 & 22.65 & 23.69 & 24.15 & 24.54 \\ \hline y & 679.5 & 707.5 & 767.1 & 817.8 & 702.3 & 903.7 & 964.9 & 1047.3 \end{array} $$ a. Obtain the equation of the estimated regression line, and discuss the extent to which the simple linear regression model is a reasonable way to relate fracture toughness to mode-mixity angle. b. Does the data suggest that the average change in fracture toughness associated with a one-degree increase in mode-mixity angle exceeds \(50 \mathrm{~N} / \mathrm{m}\) ? Carry out an appropriate test of hypotheses. c. For purposes of precisely estimating the slope of the population regression line, would it have been preferable to make observations at the angles \(16,16,18,18,20,20\), \(20,20,22,22,22,22,24,24,26\), and 26 (again a sample size of 16)? Explain your reasoning. d. Calculate an estimate of true average fracture toughness and also a prediction of fracture toughness both for an angle of 18 degrees and for an angle of 22 degrees, do so in a manner that conveys information about reliability and precision, and then interpret and compare the estimates and predictions.

Mist (airborne droplets or aerosols) is generated when metal-removing fluids are used in machining operations to cool and lubricate the tool and workpiece. Mist generation is a concern to OSHA, which has recently lowered substantially the workplace standard. The article "Variables Affecting Mist Generaton from Metal Removal Fluids" (Lubrication Engr., 2002: 10-17) gave the accompanying data on \(x=\) fluid-flow velocity for a \(5 \%\) soluble oil \((\mathrm{cm} / \mathrm{sec})\) and \(y=\) the extent of mist droplets having diameters smaller than \(10 \mu \mathrm{m}\left(\mathrm{mg} / \mathrm{m}^{3}\right)\) : $$ \begin{array}{l|ccccccc} x & 89 & 177 & 189 & 354 & 362 & 442 & 965 \\ \hline y & .40 & .60 & .48 & .66 & .61 & .69 & .99 \end{array} $$ a. The investigators performed a simple linear regression analysis to relate the two variables. Does a scatter plot of the data support this strategy? b. What proportion of observed variation in mist can be attributed to the simple linear regression relationship between velocity and mist? c. The investigators were particularly interested in the impact on mist of increasing velocity from 100 to 1000 (a factor of 10 corresponding to the difference between the smallest and largest \(x\) values in the sample). When \(x\) increases in this way, is there substantial evidence that the true average increase in \(y\) is less than .6? d. Estimate the true average change in mist associated with a \(1 \mathrm{~cm} / \mathrm{sec}\) increase in velocity, and do so in a way that conveys information about precision and reliability.

Show that the "point of averages" \((\bar{x}, \bar{y})\) lies on the estimated regression line.

The accompanying data was read from a graph that appeared in the article "Reactions on Painted Steel Under the Influence of Sodium Chloride, and Combinations Thereof"' (Ind. Engr: Chem. Prod. Res. Dev., 1985: 375-378). The independent variable is \(\mathrm{SO}_{2}\) deposition rate \(\left(\mathrm{mg} / \mathrm{m}^{2} / \mathrm{d}\right)\), and the dependent variable is steel weight loss \(\left(\mathrm{g} / \mathrm{m}^{2}\right)\). $$ \begin{array}{r|rrrrrr} x & 14 & 18 & 40 & 43 & 45 & 112 \\ \hline y & 280 & 350 & 470 & 500 & 560 & 1200 \end{array} $$ a. Construct a scatter plot. Does the simple linear regression model appear to be reasonable in this situation? b. Calculate the equation of the estimated regression line. c. What percentage of observed variation in steel weight loss can be attributed to the model relationship in combination with variation in deposition rate? d. Because the largest \(x\) value in the sample greatly exceeds the others, this observation may have been very influential in determining the equation of the estimated line. Delete this observation and recalculate the equation. Does the new equation appear to differ substantially from the original one (you might consider predicted values)?

Toughness and fibrousness of asparagus are major determinants of quality. This was the focus of a study reported in "Post-Harvest Glyphosphate Application Reduces Toughening, Fiber Content, and Lignification of Stored Asparagus Spears" (J. of the Amer. Soc. of Hort. Science, 1988: 569–572). The article reported the accompanying data (read from a graph) on \(x=\) shear force \((\mathrm{kg})\) and \(y=\) percent fiber dry weight. $$ \begin{array}{l|ccccccccc} x & 46 & 48 & 55 & 57 & 60 & 72 & 81 & 85 & 94 \\ \hline y & 2.18 & 2.10 & 2.13 & 2.28 & 2.34 & 2.53 & 2.28 & 2.62 & 2.63 \\ x & 109 & 121 & 132 & 137 & 148 & 149 & 184 & 185 & 187 \\ \hline y & 2.50 & 2.66 & 2.79 & 2.80 & 3.01 & 2.98 & 3.34 & 3.49 & 3.26 \end{array} $$ a. Calculate the value of the sample correlation coefficient. Based on this value, how would you describe the nature of the relationship between the two variables? b. If a first specimen has a larger value of shear force than does a second specimen, what tends to be true of percent dry fiber weight for the two specimens? c. If shear force is expressed in pounds, what happens to the value of \(r\) ? Why? d. If the simple linear regression model were fit to this data, what proportion of observed variation in percent fiber dry weight could be explained by the model relationship? e. Carry out a test at significance level \(.01\) to decide whether there is a positive linear association between the two variables.

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