```
require(lattice)
xyplot(Gas ~ Temp | Insul, whiteside, panel =
function(x, y, ...) {
panel.xyplot(x, y, ...)
panel.lmline(x, y, ...)
}, xlab = "Average external temperature (deg. C)",
ylab = "Gas consumption (1000 cubic feet)", aspect = "xy",
strip = function(...) strip.default(..., style = 1))
gasB <- lm(Gas ~ Temp, whiteside, subset = Insul=="Before")
gasA <- update(gasB, subset = Insul=="After")
summary(gasB)
summary(gasA)
gasBA <- lm(Gas ~ Insul/Temp - 1, whiteside)
summary(gasBA)
gasQ <- lm(Gas ~ Insul/(Temp + I(Temp^2)) - 1, whiteside)
coef(summary(gasQ))
gasPR <- lm(Gas ~ Insul + Temp, whiteside)
anova(gasPR, gasBA)
options(contrasts = c("contr.treatment", "contr.poly"))
gasBA1 <- lm(Gas ~ Insul*Temp, whiteside)
coef(summary(gasBA1))
```

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