I'm doing a research fellowship on monetary policy and taxation. It seems nearly impossible to find credible data on GDP before the 1950s. The same for the interest rate. Does anyone know where I can get it?
Don't know about interest rates, maybe the Federal Reserve Website, but in regards to GDP, and other economic data, I've previously posted a link to this website:
http://www.measuringworth.com/I'm not sure how credible their data is for GDP before the 1950s but I'd say it is at least a 'best guess.'
Unlike the whitehouse.gov website you can ask for various analysis of the data.
They also have inflation rates for the U.S back to 1775, so I guess to some degree that can be used as a proxy for the 'interest rate.' It does concern me a little that you're a research fellow yet you used the term 'interest rate' when there is both a short term interest rate set by the Federal Reserve and a long term interest rate set by the open market. It's probably more likely you are referring to the Federal Reserve set rate, but you could have meant either.
I don't know where to find historical long term interest rate information. If that is what you meant, I'd suggest emailing a chartered bank (that's a Canadian term, I don't know if it's also used in the U.S) and tell them your situation. I'm sure they have that information.
I don't mean to be a complete jerk, but in addition to not specifying whether you were asking for the short term interest rate, you also didn't state whether you wanted the nominal or real GDP rate, or even the most relevant stat of real GDP per capita. I don't state this to be a jerk, but to point out that if you have any interest in pursuing academia I'd guess that you need to be much more precise in your use of terminology.
This is certainly relevant to your asking for the interest rate, but it may even be the case that some websites only provide nominal GDP or only provide real GDP.
I know it took me years to even begin to become more precise in my use of the language to the point that I'm now occasionally accused of being a pedant.
Finally, in case this is what you are really looking for, I can save you the trouble. While according to measuringworth.com Real GDP is higher in the years before the Federal Reserve was reestablished in 1913 than in the years when there was no central bank, real GDP per capita is considerably higher (over 0.5% per year) since 1913 than in the years there was no central bank.