Karim is investigating the well-being of health care workers in his county during the COVID-19 pandemic. He notes that the health care workers in his county consist of 15% physicians, 50% nurses, and 35% administrative staff. He is considering several different sampling techniques for his study.

Karim could randomly select 15 physicians, 50 nurses, and 35 administrative staff for his sample of 100 participants.
the sampling is ?