- The number of pages in the tax code.
- The length of the form you hand in.
- The percent of tax payers who hire someone to do their taxes for them. (This may also be affected by the computer literacy of the country.)
- The number of changes in the tax law from year to year.
- The minimum amount you have to declare. (Do I need to declare my 25 cents that I won from Justin, my 8 year old great nephew, on a math game? Can he use the -25 cents as a deduction? He can use it to offset gambling gains.
- The number of items you can deduct.
There is a problem with all of these measures. What if the tax code is 100,000 pages long but 99.9% of the people only need the first page? One solution is to do some sort of weighted sum.
Deciding whether a tax system is complicated is a hard problem; however, deciding if its fair is a much harder problem.