As far as the statistics go, on the application form they ask you for what race you self-identify as. There are only a certain number of checkboxes so a 'half'

As far as the statistics go, on the application form they ask you for what race you self-identify as. There are only a certain number of checkboxes so a 'half' just has to choose which box to tick. That's the meaning behind the line in [3]: "Asian-American students face an extra source of stress : deciding whether to respond to the application question asking for their race and ethnicity."