Skidding is a major contributor to highway accidents. The following experiment was conducted to estimate the effect of pavement and tire tread depth on spinout speed, which is the speed (in mph) at...

Skidding is a major contributor to highway accidents. The following experiment was conducted to estimate the effect of pavement and tire tread depth on spinout speed, which is the speed (in mph) at which the rear wheels lose friction when negotiating a specific curve. There are two asphalt (ASPHALT1 and ASPHALT2) pavements and one concrete pavement and three tire tread depths (one-, two-, and six-sixteenths of an inch). This is a factorial experiment, but the number of observations per cell is not the same. The data are given in Table 11.21.

(a) Perform the analysis of variance using both the dummy variable and “standard” approaches. Note that the results are not the same although the differences are not very large.

(b) The tread depth is really a measured variable. Perform any additional or alternative analysis to account for this situation.

(c) It is also known that the pavement types can be characterized by their coefficient of friction at 40 mph as follows:

ASPHALT1: 0.35,

ASPHALT2: 0.24,

CONCRETE: 0.48.

Again, perform an alternative analysis suggested by this information. Which of the three analyses is most useful?