This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'The Russell periodontal index is calculated by: \nSelect and explain. \nA. Adding all the tooth scores and dividing by the number of teeth examined, B. Adding all the tooth scores and multiplying by the number of teeth examined, C. Adding all the tooth scores and dividing by 32, D. None of the above methods', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The Periodontal Index (PI) was developed by Russell A.L. in 1956, over a trial period of ten years.\nThe Russell\'s rule states that "When in doubt assign the lesser score.\nThe Periodontal Index score (PI score) per individual is obtained by adding all of the individual scores and dividing by the number of teeth present or examined.\xa0\nPI score per person = Sum of individual scores/Number of teeth present.\nRef: Soben\xa0peter, 5th edition\xa0\npg no:326', 'role': 'assistant'}]