Question

Multiple sclerosis (MS) has an overall incidence rate in the US of less than one tenth of that of lung cancer. Yet the prevalence rate of MS is much higher than that of lung cancer (the prevalence of MS is about 75 cases per 100,000 persons, versus about 40 cases per 100,000 persons for lung cancer). What is the explanation of this? (think of the bathtub or waterfall analogy)

Answer 1

ANSWER:-

(1) Even if the incidence rate is high, if the disease gets cured very fast, it prevalence will be low

(2) Even if the incidence rate is high, if the individuals rate is high,if the individuals who get the disease die sooner, then also the prevalence will be low

Here,in case of lung cancer, once the person ha got cancer, he is not expected to survive as long a person with multiple sclerosis does.

Typically, the 5 year survival rate of lung cancer is around 20%

But people with MS have much higher life expectancy.So,even if the incidence rate is high,when we measure prevalence, we only count the living individuals who are having the disease.So,the prevalence will be low for lung cancer

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