In many cases, the under-use of highly skilled workers is a reflection of the general under-use of labour. In Ireland and Japan, for example, around one in four adults with Level 3 proficiency is outside the labour force, while in the United Slates, fewer than one in five adults al this proficiency level does not participate in the labour market. Two out of three Korean adults who score at or below level 1 are employed, while in the Slovak Republic, only two in five adults with this level of proficiency are employed. These patterns may be affected by the extent of jobs available for those with very low skills, they may also reflect weak financial rewards for working, especially if interactions between the tax and benefit systems mean that low-skilled adults face high marginal effective tax rates.