Originally Posted by Bursztyn
I suppose that such information can be found in tennis databases.
By searching such a database we can get the number of matches in which players had more success on second serve than they did on first serve.
If we know the total number of matches in a database and a number of matches which fulfill this condition, we could easily calculate percentages.
Certainly, though I don't know of any database where you could run a single search through the entire data. Not a publicly accessible one, anyway.