However, skilled workers also send remittances, and the fragmentary evidence indicates that their remittances are sustained at levels above those of unskilled workers and continue for a long time, with decay not occurring until after 20 years (see section 6.4). This indicates that the economic costs of skilled migration are not as great as has been feared and are probably outweighed by the benefits, even if training is in the public sector and remittances are private (although it is impossible to accurately cost the health disadvantages of high levels of emigration). Although there are well-known general deficits in both the health sector and the education sector, little is otherwise known of the impact of migration on labour shortages in other critical areas.