## A.10 Answers to Lecture 10 tutorial

### A.10.1 Answers to Sect. 10.4.

Answers implied by H5P.

### A.10.2 Answers to Sect. 10.5

1. ‘What is the relationship between stem age and stem diameter in heather in the central north island of NZ?’ 2. Pretty good! Too many tick marks; horizontal-axis labels would be better horizontal.
3. $$r = \sqrt{0.431} = 0.6565$$, or about $$r=0.66$$. Positive linear relationship, reasonably strong. 4. $$\hat{y} = (0.311 \times 20) + 1.531 = 7.751$$. 5. Slope of $$0.311$$: For each extra year of age, the stem diameter increases by about $$0.311$$mm on average. Intercept of $$1.531$$: For stems of zero years of age, the average stem diameter is about $$1.531$$mm. This interpretation is silly. A close look at the graph shows that this is extrapolation anyway: the data only start at about 3 years of age.