Biologists studying the effects of acid rain on wildlife collected data from 163 streams in the Adirondack Mountains. They recorded the pH (acidity) of the water and the BCI, a measure of biological diversity, and they calculated R² = 27%. Here’s a scatterplot of BCI against pH:

a) What is the correlation between pH and BCI?
b) Describe the association between these two variables.
c) If a stream has average pH, what would you predict about the BCI?
d) In a stream where the pH is 3 standard deviations above average, what would you predict about the BCI?

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BCI 1500 1250 1000 750 xx x x 6.8 7.2 pH 7.6 + 8.0 X