We only report data by three income groups because the number of sectors and more income groups together would produce a number of cells with to few observations to reveal.The "no income" group contains those corporations with income less than or equal to zero. The "positive income" group is those with income greater than zero but who still have an income so low they only pay a minimum tax. (Generally below $2,000, but it can be higher if the minimum tax is a multiple of $100 becasue the filing group contains more than one corporation.) The "taxable income" group is the remainder, those who are subject to the 5% coporate income tax.