Are Domocratic Presidents Better for the Economy

Many have stated that the economy performs so much better under Democratic Presidents.  Unemployment is mostly what people car about economically.  Lets say that by this they mean unemployment is lower under Democratic Presidents.  So to lower unemployment is all we need to do is vote for Democrats for President. 

Here are some problems that with that: 

1.If the statement is based on statistical analysis it is way too small a sample.
2. If it is a principle based point then one exception would prove it wrong. 
3. Nixon was more economically democrat than was Clinton. 
4. All presidents faced different problems.
5. Warren G Harding looks best of all if you look at just the hard facts.  Random?
6. If the people who make this claim are correct then they should blame the current 9.5 percent unemployment  on Barack Obama.