Rape victims per annum 9/100,000 in Germany reported.

Cologne metro: 1,000,000.
So 90 rape victims per annum in Cologne or .25 rapes per day.

Cologne regions: 10,000,000
So 900 rape victims per annum or 2.5 in the region per day.

1 rape victim is too many. But it is not proven it was a refugee nor does it make a statistical difference against the local background rate.