Earlier quoted context omitted.
I'm not upset about what they measured. I'm upset about what they claim they learned from it and about the kinds of causation-related lemmata they (erroneously) assert in the report.
Firstly, you're critiquing a study based on a journalist's write-up about it. Secondly, you're essentially making an epistemological argument. You could apply your core argument to almost anything and come up with the assertion that the research is invalid. "Researchers tracked use-of-force incidents" -> "Researchers tracked reports of use-of-force incidents, which is factually rather different. "Researchers observed…
As a result, in a study or a journalistic write-up of said study, I wouldn't jump to the shorthand of "tracked use-of-force incidents" as opposed to "reports of use-of-force incidents".
Just because something is the best way of measuring a quantity we currently have doesn't mean it is good enough to equate the measurement with the quantity in shorthand.