Coir fiber, derived from coconut, is an eco-friendly material with great potential for use in construction. The article

“Seepage Velocity and Piping Resistance of Coir Fiber Mixed Soils” (J. of Irrig. and Drainage Engr., 2008:

485–492) included several multiple regression analyses.

The article’s authors kindly provided the accompanying data on

, and seep No. of Predictors 5 6 7 8 9 .562 .570 .572 .575 .575 MSEk 1566 1541 1535 1530 1532 Ck 19.9 11.0 9.4 8.2 10.0 Which model would you recommend? Explain the rationale for your choice.

b. The authors also considered second-order models involving predictors and . Information on the best such models starting with the variables x2, x3, x5, x6, x7, and x8 is as follows (in going from the best four-predictor model to the best five-predictor model, x8 was deleted and both x2x6 and x7x8 were entered, and x8 was reentered at a later stage):
No. of Predictors 1 2 3 4 5 .415 .541 .600 .629 .650 MSEk 2079 1636 1427 1324 1251 Ck 433 109 104 52.4 16.5 No. of Predictors 6 7 8 9 10 .652 .655 .658 .659 .659 MSEk 1246 1237 1229 1229 1230 Ck 14.9 11.2 8.5 9.2 11.0 Which of these models would you recommend, and why?
[Note: Models based on eight of the original variables did not yield marked improvement on those under consideration here.]