I think you need to re-calibrate your expectations. G.W. Bush was in office for 96 months. Of those,
70 met your criteria for "Bad", only 15 were "Good" and
zero were "Great."
In fact, there were
39 months where we lost jobs (and 1 month of zero gain/loss). I noticed you didn't even include a grade for "Below 0", which was 40% of Bush's presidency.
I'm not pointing this out to harp on Bush or because I think you will defend him. I'm just trying to establish a baseline of expectations to keep your "grading" callibrated.
It is not difficult to find technical information about the unemployment number:
http://bls.gov/news.release/empsit.tn.htm
There are two main factors that can make the unemployment number move in unusual ways. The first is simple random variation of the surveyed sample of the population. Because the survey does not sample
everyone, there is no guarantee that the people sampled are an exact representation of the total population. In statistical terms, this is called "margin of error." Unfortuantely, this term confuses a lot of people because it's not really an 'error'. A more accurate term would be margin of uncertainty.
For the unemployment figure, the margin of uncertainty is about +/- 0.19%, which means that there really is no difference between 8.2% and 8.3%.
The other factor, of course, is the number of people who are looking for work. If there is widespread perception that there are no jobs to be found, many people stop looking for work and therefore are not counted among the unemployed. When people have increased optimism that they will find a job, they re-enter the work force and then are counted among the unemployed.