The authors of the article “Long-Term Effects of Cathodic Protection on Prestressed Concrete Structures” (Corrosion, 1997: 891–908) presented a scatter plot of y
steady-state permeation flux ( A/cm2

) versus x
inverse foil thickness

(cm1

); the substantial linear pattern was used as a basis for an important conclusion about material behavior. The MINITAB output from fitting the simple linear regression model to the data follows.

The regression equation is flux
0.398 0.260 invthick Predictor Coef Stdev t-ratio p Constant 0.3982 0.5051 0.79 0.460 invthick 0.26042 0.01502 17.34 0.000 s
0.4506 R-sq
98.0% R-sq(adj)
97.7%

Analysis of Variance Source DF SS MS F p Regression 1 61.050 61.050 300.64 0.000 Error 6 1.218 0.203 Total 7 62.269 inv- Stdev. St.

Obs. thick flux Fit Fit Residual Resid 1 19.8 4.3 4.758 0.242 0.458 1.20 2 20.6 5.6 4.966 0.233 0.634 1.64 3 23.5 6.1 5.722 0.203 0.378 0.94 4 26.1 6.2 6.399 0.182 0.199 0.48

(continued at top of next column)

inv- Stdev. St.

Obs. thick flux Fit Fit Residual Resid 5 30.3 6.9 7.493 0.161 0.593 1.41 6 43.5 11.2 10.930 0.236 0.270 0.70 7 45.0 11.3 11.321 0.253 0.021 0.06 8 46.5 11.7 11.711 0.271 0.011 0.03

a. Interpret the estimated slope and the coefficient of determination.

b. Calculate a point estimate of true average flux when inverse foil thickness is 23.5.

c. Does the model appear to be useful?

d. Predict flux when inverse thickness is 45 in a way that conveys information about precision and reliability.

e. Investigate model adequacy.