Researchers investigated aspects of the anatomy of the Melina tree, Gmelina arborea, which has been introduced into wet and dry forests in Costa Rica. The researchers wanted to know if the diameter of the trees at head height was correlated with the overall height of the trees. The table shows the data for seven trees from each type of forest.

The researchers calculated the Pearson’s correlation coefficient for the two areas as:  

The critical value at p = 0.05 for samples of this size is 0.75.

a. Explain what conclusions the researchers should make from these results.

b. Explain why the researchers chose to calculate the Pearson’s correlation coefficient and not the Spearman’s rank correlation coefficient.

c. The researchers next measured the diameters of trees of the same heights in the two forests to see if their growth in width was influenced by the rainfall in the two forests.

i. State the independent and dependent variables in the investigation.

ii. Describe the method that the researchers would follow to gain results.

iii. State how the researchers would find out if the difference between the two populations of trees is significant.

Transcribed Image Text:

Dry forest diameter / cm height / m Wet forest Tree number diameter / cm height/ m 1 38.0 25.5 31.9 20.8 2 31.5 22.0 29.8 19.5 3 33.2 18.5 32.5 24.7 4 32.0 23.5 30.5 24.0 5 30.7 18.0 33.2 27.1 6 25.0 19.0 19.7 19.5 28.5 22.5 22.5 23.3 7.