Starting with the end of World War 1, what was the average unemployment rate for each United States President? Was the overall average different for Republican and Democratic presidents, and if so, by how much? The time frame can be fudged here because of available information.
IMHO this is pretty much a general reference question. Links for it abound. So I'll instead use the balance of my answer to warn you about the data. Basically, comparing unemployment numbers over that many years has lot of issues.
First off, official BLS data only goes back to 1948. Any data you get from before that will be a bit like comparing apples to oranges just due to the fact that will have been collected differently with different standards for who counts as "unemployed".
Secondly, even within that data, the definition of "unemployed" is periodically changed. The BLS now has six differenent measures of the unemployment rate (U1 - U6). Usually they report U3, but there is a lot of discussion about whether some of the higher measures are closer to how it used to be calculated.
Thirdly, this isn't really the same country it was in the '50's. Women (half the population) are now in the workforce. We are older (less non-working kids per adult, more retirees), we have many more people on things like disability, our prison population has ballooned, etc. This is why we have the 6 different measures now.
Finally, you can cherry-pick your data just by picking when you count. For instance, a lot of Democrats like to compare from WWII through the Bush Administration. That's because the presidencies immeditely before and after that period happen to have been Democrats presiding during unusually bad recessions. (They might argue both recessions started during Republician administrations, but that's beside my point). For the same reason, Republicans would like to pick a period that includes both the Great Depression and the current recession. However, they would probably not want you to go back as far as WWI, as there were no less than 2 recessions during Republican presidencies between the World Wars. Go back to 1900, and they have several more. (Of course they could likewise argue that the post-WWI recessions started under Democrat Woodrow Wilson's watch.)
Some folks will even try to snow you by quoting U3 for other presidents, then switching to the higher U6 (usually with words like "real unemployment") for a particular president they don't like. As they say, statistics don't lie, but liars use statistics.