Since the population of Milwaukee is around 600k, that should be 0.016% of people. Or you should say something like 'of people who made emergency calls' edit:

Since the population of Milwaukee is around 600k, that should be 0.016% of people. Or you should say something like 'of people who made emergency calls' edit: that second one is still problematic since we only a couple data points on the distribution of calls per capita.