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
Which of the following variables is measured on the ordinal scale- 
Select and explain. 
A. Type of anemia, B. Severity of anemia, C. Hemoglobin, D. Serum ferritin
B: Severity of anemia
Answer: B: Severity of anemia 
Explanation: When data is ranked e.g. mild, moderate, severe  → ordinal scale is used. Therefore the severity of anemia is measured on the ordinal scale.
Type of anemia can be divided into qualitative categories (Macrocytic/microcytic, hemolytic/non-hemolytic) → Nominal scale is used.
Serum ferritin and hemoglobin are quantitative variables with a possible absolute zero value → Ratio scale is used.