Database: college_completion
Question: In Yale University, what is the average number of Black students per year who were bachelor's/equivalent-seeking cohort at 4-year institutions between 2002 to 2005?
SQL: SELECT AVG(T2.grad_cohort) FROM institution_details AS T1 INNER JOIN institution_grads AS T2 ON T2.unitid = T1.unitid WHERE T1.chronname = 'Yale University' AND T2.year BETWEEN 2002 AND 2005 AND T2.race = 'B' AND T2.cohort = '4y bach'