In a study of the relationship between serum potassium concentration and ambient temperature, investigators obtained mean daily temperatures recorded in central Oxford between April 1, 1996, and Dec...

In a study of the relationship between serum potassium concentration and ambient temperature, investigators obtained mean daily temperatures recorded in central Oxford between April 1, 1996, and Dec 31, 1997 (Ulahannan et al. 1998). They also obtained details of mean daily potassium concentrations from six hospital sites and family physicians in Oxfordshire for the same time. They produced a graph similar to Figure 11.21.

1 What kind of diagram is this?

2 What is the sloping straight line on the diagram?

3 What principle is used to calculate the line which best fits the data?

4 What is meant by the symbol ‘r’?

5 Why is the value of ‘r’ wrong on the diagram?

6 What assumption is required for the tests of significance for r to be valid?

7 How would you describe the evidence for a relationship between ambient temperature and serum potassium based on this graph?