11.5 Optional questions

These questions are optional; e.g., if you need more practice, or you are studying for the exam. (Answers are available in Sect. A.11.)

11.5.1 Optional: Identifying the correct analysis

11.5.2 Optional: Reading scatterplots

This question has a video solution in the online book, so you can hear and see the solution.

Researchers in New Zealand were interested in:

...the behaviour of heather (Calluna vulgaris) in Tongariro National Park...: the potential for herbicidal control; likely changes in secondary vegetation if biological control is effective; some aspects of its demography; and, finally, whether heather acts to facilitate or impede rates of native shrub invasion of red tussock grassland.

--- Rogers (1996)

The graph in Fig. 11.8 comes from this study examining heather in the central North Island of New Zealand.

Figure 2 (top panel) from Rogers (1996)

FIGURE 11.8: Figure 2 (top panel) from Rogers (1996)

  1. Identify a possible research question being answered by the graph.
  2. Critique the graph
  3. Compute the value of \(r\), and interpret.
  4. For a stem age of \(20\) years, what does the regression model predict as the mean stem diameter?
  5. Interpret the meaning of the slope and intercept in the regression equation. Comment on these interpretations.


Rogers GM. Control, demography, and post-control response of heather in the central North Island: Part 2. New Zealand Department of Conservation; 1996. Report No.: 29.