Sensitivity and specificity

• A screening test can give a positive or negative result
• Does not imply that the patient has or does not have the disease
• The test results can be:
  • True positive (TP) = A positive test result in the presence of the disease
  • True negative (TN) = A negative test result in the absence of the disease
  • False positive (FP) = A positive test result in the absence of the disease
  • False negative (FN) = A negative test result in the presence of the disease
• Sensitivity = the ability of the test to identify the disease in those who have it
  • Equals TP / (TP + FN)
• Specificity = the ability of the test to exclude the disease in the absence of the disease
  • Equals TN / (TN + FP)