Is there any way to convert quarterly data to monthly in excel or preferably in STATA? I Next to that, how can I transform dates in excel so as to be recognized by STATA?
You can use Cubic Splines to convert quarterly data into monthly. See also the following: https://columbiaeconomics.com/2010/01/20/how-economists-convert-quarterly-data-into-monthly-cubic-spline-interpolation/
Update: Take a look at the following link too: