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
In a stable situation- 
Select and explain. 
A. Incidence = prevalence x duration, B. Prevalence = Incidence x Duration, C. Incidence = Prevalence + Duration, D. Prevalence = Incidence + Duration
B: Prevalence = Incidence x Duration
Answer: B: Prevalence = Incidence x Duration 
Explanation: prevalence refers specifically to all current cases existing at agiven point in time ,or over a period of time in a given population. Prevalence depends on 2 factors,incidence and duration of disease. Given assumption that the population is stable,and incidence and duration are unchanging ,the relationship between incidence and prevalence can be expressed as P=I*D = incidence *mean duration. Parks textbook of preventive and social medicine.K Park. Edition 23.Pg no: 61