Question 6.50
15. Researchers studying acid rain measured the acidity of precipitation in a Colorado wilderness area for 150 consecutive weeks. Acidity is measured by pH, and lower pH values mean higher acidity. The acid rain researchers observed a straight-line pattern in acidity levels over time. They reported that the regression line
fit the data well. [Data from W. M. Lewis and M. C. Grant, Acid precipitation in the western United States, Science, 207 (1980): 176–177.]
- Draw a graph of this line. Explain what the line says about how pH was changing over time.
- According to the regression line, what was the pH at the beginning of the study (weeks = 1)? At the end (weeks = 150)?
- What is the slope of the regression line? Explain what this slope says about the rate of change in pH.
15.
(a) The pH decreases as the number of weeks increases.
(b) 5.42; 4.64 (both rounded to two decimal places)
(c) −0.0053; on average, pH declined by 0.0053 per week during the study period.