What is the percentage of Harvard university's international students in 2011?
Harvard university's refers to university_name = 'Harvard University'; in 2011 refers to year = 2011; percentage of Harvard university's international students refers to pct_international_students
SELECT T1.pct_international_students FROM university_year AS T1 INNER JOIN university AS T2 ON T1.university_id = T2.id WHERE T1.year = 2011 AND T2.university_name = 'Harvard University'