To develop new clinical test, research included group of 40 patients and group o

ID: 444452 • Letter: T

Question

To develop new clinical test, research included group of 40 patients and group of 41 healthy controls. In the patient group, test was positive in 36 cases. In control group, one has got 8 positive results. Calculate sensitivity and specify of the test. Patient, described in the problem 5, has for positive test result. To rule in the diagnosis, doctor ordered to repeated test. Calculate probability, that patient is diseased, given the second test is positive, too. Discuss, whether second test was useful. Analyse all possible combination, calculating probabilities that patient is diseased, given first test is positive, but second-negative, both negative, first negative, second-positive, Summarised data in the table.

Explanation / Answer

Total number of patients (with disease)=40

True Positive=Total number of Patients who got positive result= 36

False negative=Total number of patients who got negative result= 40-36=4

Total number of healthy controls (without disease)=41

False Positive=Total number of cases in healthy control who got positive result= 8

True negative=Total number of cases in healthy control who got negative result= 41-8=33

Disease

Non Disease

Positive

36(True Positive)

8(False Positive)

Negative

4(False Negative)

33(True Negative)

Sensitivity= probability that a test will indicate 'disease' among those with the disease

Sensitivity= True Positive/(True Positive+ False negative)=36/(36+4)=36/40=0.9

Specificity= fraction of those without disease who will have a negative test result

Specificity=True Negative/(True negative+ False Positive)=33/(33+8)=0.8

Question 7 has reference to Question 5 for data which is missing