This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
An investigator into the life expectancy of IV drug abusers divides sample of patients into HIV positive and HIV negative groups. What type of data does this division constitute - 
Select and explain. 
A. Nominal, B. Ordinal, C. Interval, D. Poion
A: Nominal
Answer: A: Nominal 
Explanation: Scales can be: Qualitative: Categorical scales: Nominal : eg: names of countries . It&;s like naming or labeling . Dichotomous : eg: yes/no, presence/absence. Ordinal : severity of disease: mild/moderate/severe.eg: staging of cancer, kuppusamy socioeconomic class. Quantitative: Metric scales: Interval Ratio Note: Dichotomous is a subtype of nominal with 2 categories .