Seventeen days after the
shooting, the researchers launched a follow-up survey of those same
participants that included newly added trauma-related measures including PTSD
symptom severity; 691 agreed to participate in this second phase. Data were
collected again through online surveys 34 weeks, on average, after the campus
shooting. In fall 2009, salivary samples were collected to obtain DNA from 276
subjects of the original study population based on willingness to participate.