Question

A study of the US clinical population found that 24.1% are diagnosed with a mental disorder, 14.9% are diagnosed with an alcohol-related disorder, and 5% are diagnosed with both disorders.
(a) What is the probability that someone from the clinical population is diagnosed with a mental disorder, knowing that the person is diagnosed with an alcohol-related disorder? Please use 3 decimal places.

(b) What is the probability that someone from the clinical population is diagnosed with an alcohol-related disorder, knowing that the person is diagnosed with a mental disorder? Please use 3 decimal places.

Answer 1

Answer:

a) 0.336

b) 0.207

Step-by-step explanation:

A probability is the number of desired outcomes divided by the number of total outcomes.

We solve this problem building the Venn's diagram of these probabilities.

I am going to say that:

A is the probability that a person from the clinical population is diagnosed with mental disorder.

B is the probability that a person from the clinical population is diagnosed with alcohol related disorder.

We have that:

$A = a + (A \cap B)$

In which a is the probability that a person is diagnosed with mental disorder but not alcohol related disorder and $A \cap B$ is the probability that a person is diagnosed with both of these disorders.

By the same logic, we have that:

$B = b + (A \cap B)$

We find the values of a,b and the intersection, starting from the intersection.

5% are diagnosed with both disorders.

This means that $A \cap B = 0.05$

14.9% are diagnosed with an alcohol-related disorder

This means that $B = 0.149$

So

$B = b + (A \cap B)$

$0.149 = b + 0.05$

$b = 0.099$

24.1% are diagnosed with a mental disorder

This means that $A = 0.241$

So

$A = a + (A \cap B)$

$0.241 = a + 0.05$

$a = 0.203$

(a) What is the probability that someone from the clinical population is diagnosed with a mental disorder, knowing that the person is diagnosed with an alcohol-related disorder?

Desired outcomes:

Mental and alcohol-related disorders, which $A \cap B$. So $D = 0.05$

Total outcomes:

Alcohol-related disorder, which is B. So $T = 0.149$

Probability:

$P = \frac{0.05}{0.149} = 0.336$

(b) What is the probability that someone from the clinical population is diagnosed with an alcohol-related disorder, knowing that the person is diagnosed with a mental disorder?

Desired outcomes:

Mental and alcohol-related disorders, which $A \cap B$. So $D = 0.05$

Total outcomes:

Mental disorder, which is B. So $T = 0.241$

Probability:

$P = \frac{0.05}{0.241} = 0.207$