How does PISA assess science literacy?

The most recent round of the assessment, PISA 2015, focused on 15-year-olds’ science literacy, defined as “the ability to engage with science-related issues, and with the ideas of science, as a reflective citizen”. To succeed on the PISA science test, students had to display their mastery of three skills: explaining phenomena scientifically (based on knowledge of scientific facts and ideas), evaluating and designing scientific enquiry, and interpreting data and evidence scientifically.