Question

A pathologist knows that 14.9% of all deaths are attributable to myocardial infarctions (a type of heart disease). (Either you have myocardial infarction or you don’t)
a. Find the mean and standard deviation for the number of such deaths that will occur in typical region with 5000 deaths.









b. In one region, 5000 death certificates are examined, and it is found that 896 deaths were attributable to myocardial infarction. Is there cause for concern? Why or why not?

Answer 1

Answer:

a) The mean number is 745 and the standard deviation is 25.18.

b) 896 deaths is a significantly high number, which means that there is cause for concern.

Step-by-step explanation:

For each death, there are only two possible outcomes. Either it is attributable to myocardial infarctions, or it is not. The probability of a death being attributable to myocardial infarctions is independent of other deaths. So we use the binomial probability distribution to solve this question.

Binomial probability distribution

Probability of exactly x sucesses on n repeated trials, with p probability.

The expected value of the binomial distribution is:

$E(X) = np$

The standard deviation of the binomial distribution is:

$\sqrt{V(X)} = \sqrt{np(1-p)}$

A value X is significantly high is:

$X > E(X) + 2\sqrt{V(X)}$

In this problem:

$p = 0.149, n = 5000$

a. Find the mean and standard deviation for the number of such deaths that will occur in typical region with 5000 deaths.

$E(X) = np = 5000*0.149 = 745$

$\sqrt{V(X)} = \sqrt{np(1-p)} = \sqrt{5000*0.149*0.851} = 25.18$

The mean number is 745 and the standard deviation is 25.18.

b. In one region, 5000 death certificates are examined, and it is found that 896 deaths were attributable to myocardial infarction. Is there cause for concern? Why or why not?

Is 896 a significantly high number?

$E(X) + 2\sqrt{V(X)} = 745 + 2*25.18 = 795.36$

895 > 795.36

896 deaths is a significantly high number, which means that there is cause for concern.