4.76. Growth rate of algae. The Journal of Applied Phycology (December 1994) published research on the seasonal growth activity of algae in an indoor environment. The daily growth rate y
was regressed against temperature x using the quadratic model E(y) = β0 + β1x + β2×2. A par- ticular algal strain was grown in a glass dish indoors at temperatures ranging from 10◦ to 32◦ Celsius. The data for n = 33 such experiments were used to ﬁt the quadratic model, with the following results:
yˆ = −2.51 + .55x − .01×2, R2 = .67
(a) Sketch the least squares prediction equation. Interpret the graph.
(b) Interpret the value of R2.
(c) Is the model useful for predicting algae growth rate, y? Test using α = .05.