Still, more than a fourth of those with a university degree are informal workers - they do not contribute to the mandatory pension system. This suggests that informality may not systematically be forced by employers nor related to exclusion from the formal sector, but rather that it may be a worker’s decision, e.g. to minimise tax payments. According to this definition, about 50% of the employed population was in the informal sector in early 2012, a level which has been broadly stable since the late 1990s (Figure 1.5). The firm size column corresponds to the share of the population employed in firms of five or less persons.