krndatta wrote:
KarishmaB Ma'am,
Please help me understand some basics in this question.
The incidence rate of S is same for all age groups. This means that S can occur to any person from ages 5 to 55.
The incidence rate of A and BP increases with age. This means that as the person's age increases then the incidence of A and BP increases.
In other words, a person aged 5 to 20 might not develop A and Bp, but a person aged 55 will definitely do.
It is about probabilities. A person aged 5 to 20 will have a low probability of developing A or Bp but aged 55 will have a higher probability of developing them.
If incidence of S is the same for all age groups, it means in the set of people who have S, there will be people of all age groups. For every age, the probability is the same.
So the set of people who have S will be a sample of the population without any age bias. If there is a 20% incidence rate of S (same for all age groups) and there is a population of 100 people (20 children, 30 youth, 30 adults, 20 old), the set of people with S will likely be 20 people (4 children, 6 youth, 6 adults, 4 old). So the average age of this set of people will be similar to the average age of the population.
In contrast, note that average age of set of people having A or Bp will be higher since incidence of these diseases is higher among the older people.
_________________
Karishma
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