While there are objective measures of success with patients, a physical therapist may have additional metrics that they use. This answer can provide insight into the candidate's attitude toward their chosen field and working with patients. It can also help you understand how strictly a potential hire will adhere to policies versus adapting to a patients unique needs and individual goals. What to look for in an answer:

Discusses previous work with patients

Presence of compassion and caring when setting goals

Adaptability of candidate's approach to each individuals needs