While it was difficult for his family, they knew that placing paul in an institution would be best for his safety and well-being, since he required constant supervision due to his limited mental ability. in this case, it is most likely that paul's:

Intelligence score is below 70.

Explanation:

Intelligence score or intelligence quotient may be defined as the total score that are derived by the several tests to assess the human intelligence. Most of the world population has intelligence score between 85 to 115.

The individual that has intelligence score less than 70 indicates the individual with the mental problems. They suffers from mental disability and recognize that the individual might suffers from the  cognitive impairments. Paul's condition clear;y determines that his intelligence score is below 70%.