Question

The following table shows one month’s results from a public health clinic’s testing for a new strain of flu during a pandemic that were confirmed the following month. Examine the results and answer the first four questions.

Patients With               Patients Without

                                                            New Flu                     New Flu

Patients Testing Positive             200                            100

Patients Testing Negative             50                             700

Calculate the following probabilities:

1. P (Patient tested negative | Patient truly positive)
2. P (Patient tested positive | Patient truly negative)

Answer 1

From the given data, the following Table is calculated:

	Patients without new flu	Patients with new flu	Total
Patients testing positive	200	100	300
Patients testing negative	50	700	750
Total	250	800	1050

(a)

P (Patient tested negative | Patient truly positive) = P (Patient tested negative AND Patient truly positive) / P( Patient truly positive)

                                                                          = 700/ 800

                                                                           = 0.875

So,

Answer is:

0.875

(b)

P (Patient tested positive | Patient truly negative) = P (Patient tested positive AND Patient truly negative) / P( Patient truly negative)

                                                                      = 200/ 250

                                                                      =0.8

So,

Answer is:

0.8