Here's a Washington monthly article about political parties and economic performance:
http://www.washingtonmonthly.com/archiv ... 006282.php
It's one of many independent publications that state democratic administrations overwhelmingly show better economic performance than republican ones. I've seen raw numbers myself it's pretty undisputed that this is the case. In fact, I don't know of any conservative groups or publications that dispute this correlation but you're welcome to search around for any.
"The results are simple: Democratic presidents have consistently higher economic growth and consistently lower unemployment than Republican presidents. If you add in a time lag, you get the same result. If you eliminate the best and worst presidents, you get the same result. If you take a look at other economic indicators, you get the same result. There's just no way around it: Democratic administrations are better for the economy than Republican administrations."