Refer to the International Journal of Foresting Engineering (Vol. 19, 2008) study of neck muscle activity patterns among forestry vehicle operators, Exercises 12.23 and 12.36. 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 first-order, main effects model for E(y) as a function of dominant hand power level (x₃) and vehicle type (x₇).

b. Interpret, in the words of the problem, the value of β₂ in the model, part a.

c. Add term(s) to the model, part a, that allow for interaction between dominant hand power level and vehicle type. Sketch the relationships hypothesized by this model.

d. What function of the β’s in the model, part c, represents the change in E(y) for every 1 percent increase in dominant hand power when operating a Valmet vehicle?

e. What function of the β’s in the model, part c, represents the difference in E(y) values between the Timber jack operators and Valmet operators who have a dominant hand power level of 75% ?

f. Write the equation of a complete second-order model for E(y) as a function of dominant hand power level (x₃) and vehicle type (x₇). Sketch the relationships hypothesized by this model.

g. What function of the β’s in the model, part f, represents the rate of curvature between E(y) and dominant hand power when operating a Valmet vehicle?

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. 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:

Transcribed Image Text:

X1 = Age of operator (years) %3! x2 Duration of lunch break (minutes) %3D X3 Dominant hand power level (percentage) X4 Perceived stress at work (5-point scale) x5 = {1 if married, 0 if not} X6 = (1 if day shift, 0 if night shift} x7 = {1 if operating a Timberjack vehicle, O if operating a Valmet vehicle}