This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Non communicable diseases, Subject name: Social & Preventive Medicine
Calendar method was described by - 
Select and explain. 
A. Bitings, B. Ogino, C. Wallace, D. Ogive
B: Ogino
Answer: B: Ogino 
Explanation: Park's textbook of preventive and social medicine 23rd edition. *safe period or rhythm method, calender method first discovered by Ogino in 1930 .the method is based on the fact that ovulation occurs from 12 to 16 days before the onset of menstruation.