While the U.S. homicide rate overall has fallen in recent years, the number of active shooter events, that is where a person with a gun attempts to kill people in a confined and populated area, has increased in the U.S. since 2000. The disaster psychology literature tells us that when faced with sudden, fearful events that are unfamiliar, our natural tendency is to go into denial. This is because our brains try rapidly to find prior experience to work from, get "no search results found", then our backup plan is to look to see if anyone else has a "search hit". The psychology and neuroscience of this is described in the book The Unthinkable: who survives when disaster strikes. If we find ourselves in the midst of an active shooter event, particularly in a classroom situation, this means we will likely have one of a number of reactions, such as freezing (everyone gets in a loop of "no search results found"), thinking our senses must be giving us bad information ("that probably wasn't a gun"), or pulling out an inappropriate experience, such as treating the event as if it were a fire alarm, or making jokes. We tend to not want to be seen to be over-reacting. In an active shooter event, seconds are critical, so we cannot afford to risk this happening. This psychology was likely behind the surprisingly inappropriate responses of professors during the recent Purdue shooting incident (see Purdue Review article). Here are some steps you can take before an incident, to make sure this doesn't happen.
If you get information about an active shooter elsewhere on campus (for example through IU Notify), you should be prepared for an extended period of time with very little information. RUN-HIDE-FIGHT still applies here - if you are able to get away from campus safely without going anywhere near the scene of the shooting, this is probably the best thing. If you are running a class, and you get this kind of notification, the best approach is probably to stop class, close doors, stay away from windows, and make a RUN-HIDE-FIGHT plan with the students for if a shooter came in proximity. You should also make a plan for how to handle bathroom visits, etc. Note that we have no authority to prevent people leaving if they wish. In the instance of an active shooter alert elsewhere on campus, SOIC Emergency Response Team members will attempt to find out more information and will circulate to pass this on.
For more recommendations and information, see the IU Active Shooter page.