A new theory has been proposed. The expected percentage increase in alcoholism in each city is equal to the rate of change in the price of gold plus the product of two terms. The first is the covariance of the percentage change in alcoholism in the city with the percentage change in professors' salaries divided by the variance of the percentage change in professors' salaries. The second term is the percentage change in professors' salaries minus the percentage increase in gold. How would you test this proposition?