Before revision:  However, economists lack a robust method for estimating the tax gap through a bottom-up approach  based on fiscal audits.
After revision:  However, economists lack a robust method for estimating the tax gap through a bottom-up approach , based on results from fiscal audits, through the use of Machine Learning. The major disadvantage of bottom-up approaches is represented by selection bias when audited taxpayers are not randomly selected, as in the case of audits performed by the Italian Revenue Agency. Our proposal, based on fiscal audits.