Not everyone who needs to evacuate for their safety does so, while at the same time many people who do not need to leave for their safety do so any way. Chapter 4 summarizes the research findings regarding factors that influence decisions to evacuate or not. Influential factors include the objective, physical vulnerability of residents, perceived vulnerability, actions taken by public safety officials, awareness and interpretation of forecast information, and evacuation obstacles. The role of demographics in predicting evacuation behavior is somewhat contentious. The Protective Action Decision Model, a conceptualization of how individuals make adaptive decisions in response to hazards, is used to explain who evacuates.