Data are available for all fires in Chicago last year on x = number of firefighters at the fire and y = cost of damages due to the fire.
a. If the correlation is positive, does this mean that having more firefighters at a fire causes the damage to be worse? Explain.
b. Identify a third variable that could be a common cause of x and y. Construct a hypothetical scatter plot (like Figure 3.22 for crime and education), identifying points according to their value on the third variable, to illustrate your argument.