Increases in the mortgage interest rate increase the cost of owning a house and lower the demand for houses. In this question we consider an equation where the monthly change in the number of new one-family houses sold in the U. S depends on last month's change in the 30-year conventional mortgage rate. Let HOMES be the number of new houses sold (in thousands) and IRATE be the mortgage rate. Their monthly changes are denoted by DHOMESt = HOMESt - HOMESt-1 and DIRATEt = IRATEt - IRATEt-1. Using data from January 1992 to March 2010, we obtain the following least squares regression estimates: DHOMESt = -2.077 - 53.51DIRATEt-1

(se) (3.498) (16.98) obs = 218

9.6 (a) Interpret the estimate -53.51. Construct and interpret a 95% confidence interval for the coefficient of DIRATEt-1