# problem-3.25

problem-3.25 The wtloss data can be plotted as follows:

    > attach(wtloss)
    > cor(Weight, Days)             # close to -1
    [1] -0.9853
    > plot(Days, Weight)            # kinda linear
    > res = lm(Weight ~ Days)
    > abline(res)                   # add regression line
    > plot(Days, residuals(res))    # A trend
    > detach(wtloss)

We see from the scatterplot that a linear model may not explain the data well, despite the correlation coefficient that is close to -1. The residual plot amplifies this observation. This is to be expected as it is initially easy to lose a large amount of weight, but this gets progressively harder as there is less excess weight to shed.