the national register, and they are most likely illegal immigrants. About 15 percent of the register records contain errors, but these errors come from incorrect addresses. If someone is listed at an incorrect address in the register, this can become a problem for them should they wish to, for example, get a passport. Because people depend on the register to receive services, it tends to be fairly accurate. Statistics Netherlands defines survey populations to be the population in the register, thus that sampling frame completely fits the population. There is also a database for information to do weighting adjustments. The question of whether including illegal immigrants in the count and surveys is a problem is a decision each country has to make.