Hello everyone,

I am currently writing my thesis and been having problems with some analysis. I want to examine in an additional analysis whether the level on non-conforming tax avoidance (measured via book-tax differences = btd) is significantly lower after the corporate tax rate reduction in the U.S. Prior to this I performed a fixed effects regression of tax avoidance on firm value with panel data covering firm observations for the years 2009-2019.

The most suitable approach would probably be a difference in difference approach but I do not have a control group in my sample. Is it possible to use a t-test? I did the following but am not quite sure of the right approach. I am using Stata 14.0

Code:
generate byte reform = Year > 2017 if !missing(Year)
ttest w_btd, by(reform) level(90) unequal

Thank you very much in advance.

Lisa