Explanation:
The crime rate statistic shows the number of registered crimes divided by the number of registered residents in a country or area.
"Registered" is important here!
If you add undocumented immigrants to the calculation, the statistic is skewed:
Undocumented immigrants aren't registered as residents for the statistic, since they are, well, undocumented.
However, any crime committed by any one of them will count towards the crime rate when they're registered by the police.
So even if they were much less likely to commit crime than the resident population on average, the crime rate statistic would still increase. The denominator of the equation doesn't increase by definition, because only legal residents are counted towards the statistic. But the real number of people inside the country who may commit crimes increases.
This is important to know as context when people try to "prove" immigrants are more criminal than citizens, using the crime rate statistic.
In the US our census counts residents, not citizens.
No. It counts residents who cooperate with the census. Guess what undocumented immigrants won't be doing?
Going door to door to count people is a terrible method of kering track of people, which is why most places stopped doing that, using running registries instead. It's pretty stunning that the US only has the vaguest concept of who lives there.