I don't have the statistical information to support that, but having instructed police officers at our academy, I can tell you that as a matter of officer safety, using the risk management model, we always teach them to assume that people may have firearms. So it doesn't lessen the safety issue, because a police officer will be ever so diligent in assuming that this risk could always be there.
On September 26th, 2006. See this statement in context.