Effect of authoritative information and message characteristics on evacuation and shadow evacuation in a simulated flood event

This study examines the factors influencing shadow evacuation. A mock television evacuation order was used to experimentally manipulate the presenter level of authority and message script. The dependent measures were the judged likelihood of evacuation and the judgments of message and presenter characteristics. The participants were 186 members of the general public from Lower Hutt, New Zealand. Thirty-three percent of the participants (14% knowingly) outside the evacuation zone reported they were likely to evacuate; therefore, they were classified as shadow evacuees. Nearly three-quarters of the shadow evacuation was the result of participants incorrectly including themselves in the evacuation zone. The remaining quarter reported higher levels of concern about their safety, property, and their ability to travel as a result of flooding and traffic blocking roads, relative to others outside the zone who chose to shelter in place. The presenter's level of authority and the message script did not significantly affect the reported likelihood of evacuation; however, the perceptions of trust, clarity, and message authority increased with higher levels of presenter authority. The participants indicated they would place the greatest trust in evacuation information from the highest role within Civil Defense and Emergency Management followed by local police. Effective evacuation messages should accurately and simply convey which areas are included in the evacuation zone, and provide appropriate information to those who are not at risk to minimize unnecessary travel. Official evacuation messages should be delivered by a person in the highest role appropriate to increase trust in these messages. DOI: 10.1061/(ASCE)NH.1527-6996.0000070. (C) 2012 American Society of Civil Engineers.