*2.1. Population*

The HYS is conducted every two years to students in age Grades 6, 8, 10, or 12, primarily comprising youth ages 13 to 18 years [8]. All Washington public schools, except institutional or correctional schools, are invited to participate in the survey. Private schools can opt-in if they choose. Parents can decline their child's participation. Student participation is completely voluntary and anonymous.

Survey data from 2014 were used in analysis of this study. To create a statewide sample for 2014, Washington State schools were randomly selected by representative agencies of HYS administration (Washington State Department of Health; O ffice of the Superintendent of Public Instruction; Department of Social and Health Services' Division of Behavioral Health and Recovery; Liquor and Cannabis Board; and the contractor, Looking Glass Analytics, Inc., Olympia, Washington). A total of 35,262 students and 192 schools contributed to the statewide sample. All information obtained for this study is publicly available from www.AskHYS.net.

We limited this study to students in Grades 8, 10 and 12 surveyed in 2014 because these grades received the Forms with the questions of interest and this was the only year that all drowning prevention questions were included.
