Problem
A researcher was interested in whether the incidence of violence is lower in the presence of CCTV. They employed two research assistants (one male, one female) to sit in a bar overlooking a city centre square from 8pm-2am each night during December 2015 (before CCTV cameras were fitted) and January 2016 (after CCTV cameras were installed). The assistants were told the aim of the study, and were asked to independently count the number of violent incidents they observed, and to film them on their phones.
The total number of violent acts recorded in January (with CCTV), (7), was less than half the number observed in December (no CCTV), (16). The researcher concluded that the incidence of violence is lower in the presence of CCTV.
Which of these shortcomings does NOT apply to this study?