10.44. Example 9.10 in the previous chapter used a data set on house sales to regress Y = selling price of home (in dollars) to A = size of house

(in square feet). The prediction equation was y = -50,926 + 126.6x. Now we regard size of house as Xi and also consider X2 = whether the house is new (yes or no). The prediction equation relating y to x\ has slope 161 for new homes and 109 for older homes. This gives evidence

(a) of interaction between A| and X2 in their effects on Y

(b) of a spurious association between selling price and size

(c) of a chain relationship, whereby whether new affects size which affects selling price

(d) that size of house docs not have a causal effect on price