Clinical Epidemiology Diagnosis I

Question 1

describe accuracy vs precision (on a target)

Answer 1

Question 2

describe the equation for prevalence

Answer 2

prevalence = (TP + FN) / (TP + FP + FN + TN)

Question 3

describe the equation for accuracy

Answer 3

accuracy = (TP + TN) / (TP + FP + FN + TN)

Question 4

describe the equation for sensitivity

Answer 4

sensitivity: given that a patient has a disease, what is the probability of the patient having a positive test?

sensitivity = TP / (TP + FN)

Question 5

describe the equation for specificity

Answer 5

specificity: given that a patient doesn’t have the disease, what is the proability the patient will have a negative test? (opposite of sensitivty)

specificity = TN / (FP + TN)

Question 6

describe the equation for positive predictive value

Answer 6

PPV: given that a patient has a positive test, what is the probability that a patient will have the disease?

PPV = TP / (TP + FP)

Question 7

describe the equation for negative predictive value

Answer 7

NPV: given that a patient has a negative test, what is the probability they don’t have the disease?

NPV = TN / (FN + TN)

Question 8

describe post test likelihood given a positive test vs negative test

Answer 8

• post test likelihood given a positive test:
  
  • same as the PPV; probability that patient has disease given a positive test
• post test likelihood given a negative test:
  
  • 1 - NPV; probability that patient has disease despite negative findings