Family members of an 89-year-old man bring him to a geriatric clinic because they are afraid that he is acquiring dementia owing to recent memory deterioration. The attending physician employs a new cognitive test (test X) to help rule out dementia. The test result for the patient is negative. A research examining the efficacy of test X in a sample of 200 adults aged 85, where dementia prevalence is 50%, found that the test had a specificity of 80% and a sensitivity of 90%. What is the likelihood that this patient does not have dementia if his or her pretest probability of having dementia is equal to the disease prevalence in the study population?

Question

Family members of an 89-year-old man bring him to a geriatric clinic because they are afraid that he is acquiring dementia owing to recent memory deterioration. The attending physician employs a new cognitive test (test X) to help rule out dementia. The test result for the patient is negative. A research examining the efficacy of test X in a sample of 200 adults aged >85, where dementia prevalence is 50%, found that the test had a specificity of 80% and a sensitivity of 90%. What is the likelihood that this patient does not have dementia if his or her pretest probability of having dementia is equal to the disease prevalence in the study population?

Quizplus · Accepted Answer

Eductional Objective: Negative predictive value (NPV) represents the probability of not having a disease given a negative test result. NPV is inversely proportional to the prevalence of a disease. When a patient has characteristics similar to the overall population (eg, age, sex, risk factor status), the disease prevalence is a valid estimate of the pretest probability of disease.

Family Members of an 89-Year-Old Man Bring Him to a Geriatric