Refer to the International Journal of Foresting Engineering (Vol. 19, 2008) study of neck muscle activity patterns among forestry vehicle operators, Exercise 12.23. Recall that the researchers identified the key explanatory variables of y = the number of sustained low-level muscle activity (SULMA)  periods exhibited by an operator that exceed 8 minutes. A list of the potential predictors is reproduced below:

a. Write the equation of a model for E(y) as a function of  the day/night shift qualitative independent variable.

b. Which of the β’s in the model, part a, represents the difference in E(y) values between the day shift and night shift operators?

c. Write the equation of a model for E(y) as a function of the vehicle type qualitative independent variable.

d. If the β multiplied by x₇ in the model, part c, is negative, what does this imply practically?

Data from Exercise 12.23

Research in the International Journal of Foresting Engineering (Vol. 19, 2008) investigated the muscle activity patterns in the neck and upper extremities exhibited during a work day among forestry vehicle operators. For one portion of the study, the researchers compared the muscle activity of operators of two types of harvesting vehicles—Timber jack and Valmet. (See Exercise 7.38.) In another part of the study, the researchers identified the key explanatory variables of the number of sustained low-level muscle activity (SULMA) periods exhibited by an operator that exceed 8 minutes. A list of the potential predictors is provided below:

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Age of operator (years) x2 = Duration of lunch break (minutes) X1 %3! X3 = Dominant hand power level (percentage) %3D X4 = Perceived stress at work (5-point scale) %3! X5 = (1 if married, 0 if not} X6 = (1 if day shift, 0 if night shift} {1 if operating a Timberjack vehicle, 0 if operating a X7 Valmet vehicle}