The choice between the different assessment units is relevant for a number of - partially competing - policy objectives. Rosen (1977) has shown that an income tax cannot be progressive and also achieve both horizontal equity with respect to family income (same tax burden for families with the same total income) and marriage neutrality (same tax burden regardless of marital status). However, as long as income taxes are progressive, and ignoring employment gains and behavioural effects, assessing taxes based on family incomes is superior in terms of reducing the inequality of income as measured in this study. A table with summaries of 2005 social security contribution schedules (and also of other benefits and taxes considered in this section) is available in OECD (2007a) and through www.oecd.org/els/ sorial/worfeincentiues.