[Mtinie]

A good question. 145,070,000 tax returns were processed through September 2017[1]. If the rate was one return out of every two hundred, there would have been ~725,000 audits conducted.

Multiple sources I found online reported “just over 1 million audits were conducted in 2016” (~1/120) but the number was expected to go down in 2017 due to budgetary reasons.

It is reasonable to extrapolate this value and find it in line with the original “1/200 returns”, out of the total population of filed returns.

[1] https://www.irs.gov/newsroom/filing-season-statistics-for-we...