In particular it was not easy to trace income sources; ordinary middle-income salary earners have clear, traceable sources, while high-income earners have more opportunities to take advantage of legal loopholes or to hide their income sources. This places a higher proportion of the tax burden on middle and low-income taxpayers.
反過來說，高所得家庭，所得來源不以薪資為最大宗，自行執業和投資所得的比例較高，一方面既可享受合法的減免；一方面又可藉機逕行逃漏，雙管齊下，使得較高比例的綜合所得稅負擔，反而落在中低水準的薪資所得者身上。