Stewart reports is a political polling company that has been criticized by others in the polling industry for being biased favorably towards democrats

Stewart reports is a political polling company that has been criticized

by others in the polling industry for being biased favorably towards democrats. To test whether this is true , a researcher looks at every political race the Stewart Reports predicted for the 10 years. In each race the difference between predicted and actual percent of votes recieved by the democrats candidates was calculated as X stewart -Xactual. The mean of the difference was calculated. What should be the null and alternative hypothesis to test whether on average, Stewart was over predicting democrat support?