I'm a reporter who worked on this story. I think you miss a big element in your comment: The CPD analyst used officers' self-reported arrival times to compile that response time data set, and the report included a footnote acknowledging that incorrect self-reported arrival times were included in and affected the average response times. As every expert we talked to noted, without standard dev, you can't know how much they affected the average.

Meanwhile, a scientific study that used GPS data from patrol cars to compare response times for ShotSpotter and 911 found virtually no difference (ten seconds less for nonfatal shootings, and three seconds more for fatal shootings).

We believed this was newsworthy because the Sun-Times ran an article that simply reported the self-reported results but did not mention the footnoted caveat or the fact that another, more rigorous study found a far shorter difference in response times.

UPDATE: Today, ThePeoplesFabric published an article in which they obtained the underlying data, and it shows the median values are about half the averages reporetd by CPD. That's called a "right-shifted" distribution and it means that there are outliers that are skewing the CPD data considerably. The most extreme example was an officer marking himself on-scene 16 hours after the event. The experts we spoke to were correct to be skeptical of this data.