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: Social & Preventive Medicine
Age is an example of which of the following scales? 
Select and explain. 
A. Nominal, B. Ordinal, C. Interval, D. Ratio
D: Ratio
Answer: D: Ratio 
Explanation: Metric scale is fuher divided into interval and ratio scales. In a ratio scale, there is a definite zero point and it is correct to say that an age of 6 years is twice that of 3 years. Ref: Medical biostatistics, 1st edition pg: 99