Nationality law can have a significant impact on the measurement of the national and foreign populations. In France and Belgium, for example, where foreigners can fairly easily acquire the nationality of the country, increases in the foreign population through immigration and births can eventually contribute to a significant rise in the population of nationals. On the other hand, in countries where naturalisation is more difficult, increases in immigration and births among foreigners manifest themselves almost exclusively as growth in the foreign population. In addition, changes in rules regarding naturalisation can have significant impact. For example, during the 1980s, a number of OECD countries made naturalisation easier and this resulted in noticeable falls in the foreign population (and rises in the population of nationals).