A study of atmospheric pollution on the slopes of the Blue Ridge Mountains (Tennessee) was conducted. The levels of lead (Y) found in 70 fern moss specimens (in micrograms of lead per gram of moss tissue) were collected from the mountain slopes, as well as the elevation of the moss specimen X_1 (in feet) and the direction X_2 (1 if east, 0 if west) of the slope face. call:
lm(formula = y ~ x1 + x2 + x1 * x2, data = data)
coefficients:
a) Write the equation of the model relating mean lead level to elevation and the slope face that includes an interaction between elevation and slope face in the model.
b) Write the estimated equation of the model in part a).
c) In terms of the beta's of the model in part a), give the change in lead level for every one foot increase in elevation for moss specimens on the east slope.
d) Is the overall model statistically useful for predicting lead level? Test using alpha = 0.10.