The data used to estimated the missing tax is the discrepancy between outgoing vs ingoing, ie that more stuff is being paid than should be possible with the available capital in the national economy. According to the tax office official data, the global worth of undeclared income was 150 000 MSK in 2014, 5% of BNP, for which 42.5% would have gone to taxes.

Looking at the system at that level will not be 100% but then the numbers are rounded anyway. The question I ask in the context of this discussion is if the 96% as estimated by the Swedish Tax Agency, is bigger or smaller than the 83.1% provided by IRS, knowing that both number include a certain amount of uncertainty. Both numbers are provided by the state agency of each country so some assumption of good-faith and competency should be applied.

It seems important to mention that the study looks at the behaviour of a few hundred people in Italy and Sweden playing a _game_ which simulates earning money, paying tax and possibly being audited. I.e. the study is not actually about the compliance rate of real taxation.

tptacek's description of the paper he cites, i.e. "Here's a study comparing Sweden's compliance rate with that of Italy's, and finding them roughly similar" leaves out the crucial point that the whole paper is about a game, not real taxes.