This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
Denominator of negative predictive value is 
Select and explain. 
A. TP + FP, B. TP + FN, C. TN + FN, D. TN + FP
C: TN + FN
Answer: C: TN + FN 
Explanation: Predictive value reflects the diagnostic power of the test. It&;s accuracy depends on sensitivity, specificity and disease prevalence. Predictive value of a negative test = d/(c+d)x100 Ref: 25th edition, Park&;s Textbook of Preventive and Social Medicine, Page no. 152