If the controversial citations in the article you cited are true (which I haven't read in detail, but seem questionable at a glance.) - unless the predominant amount of individuals immigrating into Spain/Norway are coming from countries with lower average IQs I would not expect it to have an effect on the average IQ of Spain/Norway.
It also stands to reason that there is no reason to assume Spain is at the top of the chart when it comes to national average - so they are most likely also having immigration from countries with a higher average. This would mitigate the effect of countries with a lower average, would it not?
Returning to the original point:
Because immigration usually entails an amount of merit and ability - the successful immigrants are usually at the higher end of the capability spectrum of the originating countries population.
Doesn't it stand to reason immigration would have either a minuscule or positive effect on national average IQ?
Maybe pre-2015, but since the European Migrant Crisis, there has been a disproportionate amount of migration from sub-Saharan Africa, which is the region that scores lowest in those surveys.
It also stands to reason that there is no reason to assume Spain is at the top of the chart when it comes to national average - so they are most likely also having immigration from countries with a higher average. This would mitigate the effect of countries with a lower average, would it not?
Returning to the original point:
Because immigration usually entails an amount of merit and ability - the successful immigrants are usually at the higher end of the capability spectrum of the originating countries population.
Doesn't it stand to reason immigration would have either a minuscule or positive effect on national average IQ?