Willis , Henry H ., Tighe , Mary , Lauland , Andrew , Ecola , Lissa , Shelton , Shoshana R ., Smith , Megan L ., Rivers , John G ., Leuschner , Kristin J ., Marsh , Terry , & Gerstein , Daniel M . 2018 .“ Homeland Security National Risk Characterization : Risk Assessment Methodology .” Rand Corporation .” Accessed March 6 , 2020 .
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