An economist believes that the percentage of the popular vote received by the incumbent party’s candidate for president depends (negatively) on the unemployment rate and (negatively) on the rate of inflation. Having read only the chapter on simple regression, he estimates an equation with voting percent as the dependent variable and the unemployment rate as the explanatory variable and ignores the rate of inflation. He obtains a positive estimate of β, indicating that an increase in the unemployment rate increases the vote received by the incumbent party. How might the omission of the rate of inflation explain this wrong sign? Be specific.