If taxpayers responded only to the expected cost of evading taxes, evasion would be far more widespread. The reason is that only about 7 percent of all tax returns are audited (over a 7 year period), and typically the penalty on under reported income is only about 20 percent of the taxes owed. Virtually no one is sent to jail simply for evading taxes unless that evasion is on a very large scale, or involves massive fraud. If a person were to evade $1,000 in taxes, his expected gain would be 0.93x$1000 -0.07x$200 (=$1000/5) = $916. On these considerations alone, he should not hesitate to evade paying the $1,000, and presumably much more.
To be sure, the expected gain is not the right criterion since most taxpayers would be risk averse regarding audits and punishments, especially if there is some chance of much greater than the average punishment or likelihood of an audit. However, if the expected gain from evading $1,000 were $916, the degree of risk aversion would have to be huge, far higher than the risk aversion that is embodied in pricing of assets, for risk to explain why there is so little tax evasion.
Could the explanation be most people underestimate the return to tax evasion, because the IRS persecutes anyone who tries to raise the public's awareness?