[Developing countries] In developing countries the tax administration does not always carry out the intent of tax legislation, but makes its own policy. On average, about 70% or more of the tax revenue of the majority of developing countries comes from indirect taxes (customs duties, for example). Since many indirect taxes tend to be both regressive in incidence and inelastic in yield as income rises, their preponderance in the tax structure calls for frequent revisions of the basic rate structure if the share of tax revenue in total income is to be maintained, for which revisions the developing countries are administratively ill equipped. In addition, although most developing countries levy direct taxes on income, defective legislation and inefficient administration mean that tax collections fall far short of amounts due. In many countries there is no single comprehensive tax on all income except the regular system of income taxation, which leaves important sources untaxed.