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The paper "Biomechanical Characteristics of the Final Approach Step, Hurdle, and Take-Off of Elite American Springboard Divers" (Journal of Human Movement Studies [1984]: 189-212) gave the following data on \(y=\) judge's score and \(x=\) length of final step (in meters) for a sample of seven divers performing a forward pike with a single somersault: $$ \begin{array}{cccccccc} y & 7.40 & 9.10 & 7.20 & 7.00 & 7.30 & 7.30 & 7.90 \\ x & 1.17 & 1.17 & 0.93 & 0.89 & 0.68 & 0.74 & 0.95 \end{array} $$ a. Construct a scatterplot. b. Calculate the slope and intercept of the least-squares line. Draw this line on your scatterplot. c. Calculate and interpret the value of Pearson's sample correlation coefficient.

Short Answer

Expert verified
The scatterplot displays the relationship between the length of the final step and the judge's score. The slope and intercept of the least-squares line can be found using their respective formulas, these give the prediction equation. The Pearson's correlation coefficient is calculated using its formula and gives a measure of the strength and direction of the correlation. Exact numerical values would require actual calculations.

Step by step solution

01

Constructing the scatterplot

This step requires plotting the points on a two-dimensional space and then visually inspecting the plot to identify any patterns or relationships. `For each diver, the \(x\), length of final step, represents the value on the horizontal axis and the \(y\), judge鈥檚 score, represents the value on the vertical axis. For example, for the first diver, plot a point at (1.17, 7.40). Repeat for the remaining divers.
02

Calculating the slope and intercept of the least-squares line

The least squares line, also known as the line of best fit, minimizes the sum of the squared residuals between the actual and predicted values.Calculate the mean of \(x\) and \(\y\) first. Let's denote them as \(\bar{x}\) and \(\bar{y}\).The slope \(b\) is calculated using the formula:\[b = \frac{\sum_{i=1}^{n} (x_i - \bar{x})(y_i - \bar{y})}{\sum_{i=1}^{n} (x_i - \bar{x})^2}\]where \(x_i\) and \(y_i\) are the individual \(x\) and \(y\) values.The intercept \(a\) is calculated using the formula:\[a = \bar{y} - b\bar{x}\]Then draw the least-squares line on the scatterplot based on the calculated values of slope and intercept.
03

Calculating and interpreting the value of Pearson's sample correlation coefficient

The Pearson's correlation coefficient is a measure of the linear correlation between two variables \(x\) and \(y\) and is given by the formula:\[r = \frac{\sum_{i=1}^{n} (x_i - \bar{x})(y_i - \bar{y})}{\sqrt{\sum_{i=1}^{n} (x_i - \bar{x})^2 \sum_{i=1}^{n} (y_i - \bar{y})^2}}\]where \(x_i\) and \(y_i\) are individual \(x\) and \(y\) values and \(\bar{x}\) and \(\bar{y}\) are their means. The value of \(r\) lies between -1 and 1. Closer to -1 suggests strong negative correlation, closer to 1 suggests strong positive correlation and closer to 0 suggests weaker correlation.

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Key Concepts

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

Scatterplot Construction
Understanding scatterplot construction is an essential skill for analyzing relationships between two variables. It is a form of data visualization that represents individual data points in a two-dimensional graph. To create a scatterplot, two axes are designated: one for the independent variable and one for the dependent variable.

In the context of biomechanical statistics, such as evaluating divers鈥 performance, the length of the final step could be mapped on the horizontal axis (x-axis) while the judges鈥 scores can be placed on the vertical axis (y-axis). Each diver's performance is then represented as a point in this plane, located according to their step length and score. For instance, a diver who made a step of 1.17 meters and received a score of 7.40 would be plotted at the coordinates (1.17, 7.40). This plot enables us to see at a glance whether there's an apparent trend or pattern, such as whether longer steps generally lead to higher scores.

To enhance interpretation, it's common to calculate and add the least-squares line, which shows the trend and the correlation between the two variables more clearly, but we will cover that in the next section.
Least-Squares Line
The least-squares line, also referred to as the line of best fit, serves as a mathematical model to interpret the correlation between two variables on a scatterplot. It is the line that best represents the distribution of points on the graph by minimizing the sum of the squares of the vertical distances (residuals) of the points from the line.

The process to calculate the least-squares line involves finding the slope (b) and y-intercept (a) of the line. The slope indicates the direction and steepness of the line, while the intercept is where the line crosses the y-axis. The formulas to calculate the slope and y-intercept utilize the means of the x and y values along with their individual discrepancies from these means.

Once the slope and intercept have been calculated, this line can then be drawn on the scatterplot and serves as a tool to predict outcomes. In the case of the divers, the least-squares line would help to predict a judge鈥檚 score based on the length of a diver鈥檚 final step, based on the existing data. This line provides a clear visual representation of whether, and how strongly, the two variables are related.
Biomechanical Statistics
Biomechanical statistics involve the quantitative analysis of biological and mechanical data, a key tool in sports science and related fields. In the study of diving, researchers might employ these statistics to examine how physical measurements, such as the length of a diver's final step, correlate with performance outcomes like judges鈥 scores.

Pearson's correlation coefficient (denoted as r) is a measure used in biomechanical statistics to determine the strength and direction of a linear relationship between two continuous variables. The coefficient ranges from -1 to 1, with values close to 1 indicating a strong positive correlation, -1 indicating a strong negative correlation, and values near 0 suggesting no linear correlation.

To interpret this in a practical scenario, a higher Pearson's correlation coefficient (closer to 1) between step length and scores in a diving competition would suggest that as one increases, so does the other. Conversely, a value closer to -1 would suggest that as one variable increases, the other decreases. As such, Pearson鈥檚 correlation coefficient provides a numeric summary of how two factors are related and is a vital tool in biomechanical studies.

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Most popular questions from this chapter

The paper "Crop Improvement for Tropical and Subtropical Australia: Designing Plants for Difficult Climates" (Field Crops Research [1991]: 113-139) gave the following data on \(x=\) crop duration (in days) for soybeans and \(y=\) crop yield (in tons per hectare): $$ \begin{array}{rrrrrr} x & 92 & 92 & 96 & 100 & 102 \\ y & 1.7 & 2.3 & 1.9 & 2.0 & 1.5 \\ x & 102 & 106 & 106 & 121 & 143 \\ y & 1.7 & 1.6 & 1.8 & 1.0 & 0.3 \end{array} $$ $$ \begin{gathered} \sum x=1060 \quad \sum y=15.8 \quad \sum x y=1601.1 \\ a=5.20683380 \quad b=-0.3421541 \end{gathered} $$ a. Construct a scatterplot of the data. Do you think the least-squares line will give accurate predictions? Explain. b. Delete the observation with the largest \(x\) value from the sample and recalculate the equation of the least-squares line. Does this observation greatly affect the equation of the line? c. What effect does the deletion in Part (b) have on the value of \(r^{2}\) ? Can you explain why this is so?

Athletes competing in a triathlon participated in a study described in the paper "Myoglobinemia and Endurance Exercise" (American Journal of Sports Medicine [1984]: 113-118). The following data on finishing time \(x\) (in hours) and myoglobin level \(y\) (in nanograms per milliliter) were read from a scatterplot in the paper: $$ \begin{array}{rrrrrr} x & 4.90 & 4.70 & 5.35 & 5.22 & 5.20 \\ y & 1590 & 1550 & 1360 & 895 & 865 \\ x & 5.40 & 5.70 & 6.00 & 6.20 & 6.10 \\ y & 905 & 895 & 910 & 700 & 675 \\ x & 5.60 & 5.35 & 5.75 & 5.35 & 6.00 \\ y & 540 & 540 & 440 & 380 & 300 \end{array} $$ a. Obtain the equation of the least-squares line. b. Interpret the value of \(b\). c. What happens if the line in Part (a) is used to predict the myoglobin level for a finishing time of \(8 \mathrm{hr}\) ? Is this reasonable? Explain.

For each of the following pairs of variables, indicate whether you would expect a positive correlation, a negative correlation, or a correlation close to \(0 .\) Explain your choice. a. Maximum daily temperature and cooling costs b. Interest rate and number of loan applications c. Incomes of husbands and wives when both have full- time jobs d. Height and IQ e. Height and shoe size f. Score on the math section of the SAT exam and score on the verbal section of the same test g. Time spent on homework and time spent watching television during the same day by elementary school children h. Amount of fertilizer used per acre and crop yield (Hint: As the amount of fertilizer is increased, yield tends to increase for a while but then tends to start decreasing.)

The paper "A Cross-National Relationship Betwee Sugar Consumption and Major Depression?" (Depression and Anxiety [2002]: \(118-120\) ) concluded that there was a correlation between refined sugar consumption (calories per person per day) and annual rate of major depression (cases per 100 people) based on data from 6 countries. $$ \begin{array}{lcc} \text { Country } & \text { Consumption Rate } \\ \hline \text { Korea } & 150 & 2.3 \\ \text { United States } & 300 & 3.0 \\ \text { France } & 350 & 4.4 \\ \text { Germany } & 375 & 5.0 \\ \text { Canada } & 390 & 5.2 \\ \text { New Zealand } & 480 & 5.7 \\ & & \\ \hline \end{array} $$ a. Compute and interpret the correlation coefficient for this data set. b. Is it reasonable to conclude that increasing sugar consumption leads to higher rates of depression? Explain. c. Do you have any concerns about this study that would make you hesitant to generalize these conclusions to other countries?

Percentages of public school students in fourth grade in 1996 and in eighth grade in 2000 who were at or above the proficient level in mathematics were given in the article 鈥淢ixed Progress in Math鈥 (USA Today, August 3, 2001) for eight western states: $$ \begin{array}{lcc} \text { State } & (1996) & \text { (2000) } \\ \hline \text { Arizona } & 15 & 21 \\ \text { California } & 11 & 18 \\ \text { Hawaii } & 16 & 16 \\ \text { Montana } & 22 & 37 \\ \text { New Mexico } & 13 & 13 \\ \text { Oregon } & 21 & 32 \\ \text { Utah } & 23 & 26 \\ \text { Wyoming } & 19 & 25 \\ \hline \end{array} $$ a. Construct a scatterplot, and comment on any interesting features. b. Find the equation of the least-squares line that summarizes the relationship between \(x=1996\) fourth-grade math proficiency percentage and \(y=2000\) eighth-grade math proficiency percentage. c. Nevada, a western state not included in the data set, had a 1996 fourth- grade math proficiency of \(14 \%\). What would you predict for Nevada's 2000 eighth-grade math proficiency percentage? How does your prediction compare to the actual eighth-grade value of 20 for Nevada?

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