Question 1
Paper 2Hard16 marksAn environmental science team records water clarity and aquatic plant cover at eight ponds in one catchment. The team wants to investigate the association between these variables.
| Pond | Water clarity (cm) | Aquatic plant cover (%) |
|---|---|---|
| A | 10 | 12 |
| B | 20 | 18 |
| C | 30 | 25 |
| D | 30 | 31 |
| E | 40 | 39 |
| F | 50 | 45 |
| G | 60 | 52 |
| H | 200 | 10 |
Field notes state that pond H was recently dredged. Measurements at H were repeated and agreed.
Show that ponds C and D are each assigned a clarity rank of 3.5 when the clarity values are ranked from smallest to largest.
Using all eight ponds and your GDC, determine Pearson’s product moment correlation coefficient, and Spearman’s rank correlation coefficient, Give both coefficients to three significant figures.
Calculate and again, using the seven ponds other than H. Give both coefficients to three significant figures.
A researcher claims that the full-data Pearson coefficient proves there is no association between clarity and plant cover. The researcher also claims that H should be removed as an outlier and that the Pearson coefficient for the remaining ponds should be reported as the relationship.
Discuss these claims and recommend how the results should be reported. Refer to the coefficients and the field notes.