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Oil and residuals The Trans-Alaska Oil Pipeline is a tube that is formed from 1/2-inch-thick steel and carries oil across 800miles of sensitive arctic and subarctic terrain. The pipe segments and the welds that join them were carefully examined before installation. How accurate are field measurements of the depth of small defects? The figure below compares the results of measurements on 100defects made in the field with measurements of the same defects made in the laboratory. The line y=x is drawn on the scatterplot.

(a) Describe the overall pattern you see in the scatterplot, as well as any deviations from that pattern.

(b) If field and laboratory measurements all agree, then the points should fall on the y=x line drawn on the plot, except for small variations in the measurements. Is this the case? Explain.

(c) The line drawn on the scatterplot (y=x) is not the least-squares regression line. How would the slope and y-intercept of the least-squares line compare? Justify your answer.

Short Answer

Expert verified

Part (a) There is a linear association between the two variables. For small values of laboratory measurement, the line fits very well but for higher values of laboratory, measurement points deviate much from the line.

Part (b) No, the points do not fall on they=x the line drawn on the plot

Part (c) Slope decreases, y-intercept increases.

Step by step solution

01

Part (a) Step 1: Given information

02

Part (a) Step 2: Concept

A regression line is a straight line that depicts the change in a response variable y when an explanatory variable xchanges. By putting this xinto the equation of the line, you may use a regression line to predict the value of yfor any value of x

03

Part (a) Step 3: Explanation

The general pattern moves from bottom left to higher right, as shown in the graph. In other words, higher laboratory measurement usually translates into higher field measurement. Between the two variables, there is a positive linear relationship. The line fits quite well for small values of laboratory measurement, while measurement points depart greatly from the line for larger values of laboratory measurement.

04

Part (b) Step 1: Explanation

Let's start with the scatterplot displayed here: if all field and laboratory measurements agree that each and every data point should sit exactly on this line, the field and laboratory measurements will be perfectly correlated. This is not the case in this illustration. In comparison to tiny measurements, variance is high for bigger values of measurement. As a result, the points do not fall on the plot's y=x line. Because the scatterplot's points to the right all fall below the line y=x (except for one), the points do not roughly fall one y=x line, implying that field and laboratory data may differ.

05

Part (c) Step 1: Explanation

When y = x is compared to the least-square line y=a+bx, the y-intercept is 0and the slope is 1When the explanatory variable x=0, the predicted response of y=0is shown as intercept=0Slope=1 indicates that as the explanatory variable x varies, the expected response ofychanges along the line. When x grows by one unit, y increases by one unit.

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