I make this comment almost every time that this comes up. The Earned Income Tax Credit (EITC) is a ~$70-100bn social payments / anti-poverty program for lower-

I make this comment almost every time that this comes up. The Earned Income Tax Credit (EITC) is a ~$70-100bn social payments / anti-poverty program for lower-paid Americans masquerading as a refundable tax credit. So the IRS ends up running that, because the IRS is responsible for tax, despite the fact that virtually none of the recipients of EITC actually owe any income tax in the first place. Congress has made the EITC fairly complicated, specifically relating to the relationship between the person claiming the credit and their dependent children. Some of that is natural, given it's actually a anti-poverty spending program. The net result is that the EITC isn't just a simple "I made this much, and this is how much tax I owe as a result" thing. It's got eligibility requirements, it's got cross-checks to make sure that multiple returns aren't claiming the same dependent children, it's got checks to see the dependent children actually exist etc. It's not surprising that filers make errors at a higher rate for more complex filings, and it's therefore also not a surprise that the IRS automates error-checking. EITC auditing is also highly effective, with changes to returns being made in ~90% of cases where the IRS challenges the return.