In the Dutch senate elections, how is the weighting for the electoral college for non-residents determined?

Question

In The Netherlands, the Senate is elected by members of the provincial parliaments as well as the electoral colleges for the Senate, where the electoral colleges represent voters who do not live in a Dutch province. The voting for the provinces and the electoral college of the Caribbean Netherlands is weighted based on the population in each province or Caribbean municipality.

How is the weighting determined for the electoral college of non-residents (in other words: Dutch citizens living abroad)? I found that the number of members is determined by the number of registered voters, but I could not find how the vote of those members in the Senate elections is weighted in relation to those of the provincial parliaments or the electoral college of the Caribbean Netherlands. Is it based on the total number of registered voters? The number of voters registered for this particular election? The total number of residents living abroad (is that even known?)? The number of voters voting in the election? Something else?

Answer 1

Indeed the total weight of votes from a province or Caribbean municipality is proportional to the population of those areas, save for rounding errors introduced because of the indirect nature of the election.

Because the total number of Dutch citizens living abroad—the so-called "niet-ingezetenen"—is not known, the number of registered voters from this group is used to estimate the total number of people. To do this, the ratio of citizens to registered voters of the niet-ingezetenen is taken to be equal to the ratio of inhabitants to eligible voters of the provinces and Caribbean territory.

Of course inhabitants isn't quite the same citizens, and eligible voters is not the same as registered voters. Regardless, this is how the calculation works.

Sources: The relevant law and an explanation from the Dutch election authority (in the dropdown under "Kiescollege niet-ingezetenen").