34.8 Exercises

Selected answers are available in Sect. D.31.

Exercise 34.1 Draw a scatterplot with:

  1. A negative correlation coefficient, with the value of \(r\) very close to (but not equal to) \(-1\).
  2. A positive correlation coefficient, with the value of \(r\) very close to (but not equal to) \(+1\).
  3. A correlation coefficient very close to \(0\).

Exercise 34.2 A study (Myers (1990), p. 75) of American footballers measured the right-leg strengths \(x\) of 13 players (using a weight lifting test), and the distance \(y\) they punted a football (with their right leg) (Fig. 34.11).

  1. The value of the correlation coefficient is 0.881. Compute the value of \(R^2\), and explain what this means.
  2. jamovi was used to study the correlation (Fig. 34.12). Using this output, perform a hypothesis test to determine if a correlation exists between punting distance and right-leg strength.
Punting distance and right leg strength

FIGURE 34.11: Punting distance and right leg strength

jamovi output for the punting data

FIGURE 34.12: jamovi output for the punting data

Exercise 34.3 A study examined the time taken to deliver soft drinks to vending machines (Montgomery and Peck 1992) using a sample of size \(n=25\) (Fig. 34.13). To perform a test of the correlation coefficient, are the statistical validity conditions met?
The time taken to deliver soft drinks to vending machines

FIGURE 34.13: The time taken to deliver soft drinks to vending machines

Exercise 34.4 A study of hot mix asphalt (Panda, Das, and Sahoo 2018) created \(n=42\) samples of asphalt and measured the volume of air voids and the bitumen content by weight (Fig. 34.14).

  1. Using the plot, estimate the value of \(r\).
  2. The value of \(R^2\) is 99.29%. What is the value of \(r\)? (Hint: Be careful!)
  3. Would you expect the \(P\)-value testing \(H_0\): \(\rho=0\) to be small or large? Explain.
  4. Would the test be statistically valid?
Air voids in bitumen samples

FIGURE 34.14: Air voids in bitumen samples