Ms Josephine Feehily:

The effective rate will be reduced through reference to tax credits and reliefs. Capital allowances would be one. In recent times, the research and development tax credit has frequently been used. That is encouraged as a matter of tax policy. It is also encouraged in Europe because research and development is considered to be particularly important in these times.

Those are the two that come to mind but there are a range of credits available to businesses, whether multinationals or other businesses, which reduce their effective rate. Similarly with citizens, medical relief, mortgage interest relief and so on reduce one's headline rate to an effective rate.