Sensitivity/Specificity Practice Questions

Question 1

A group of investigators who are studying individuals infected with Trypanosoma cruzi is evaluating the ELISA absorbance cutoff value of serum samples for diagnosis of infection. The previous cutoff point is found to be too high, and the researchers decide to lower the threshold by 15%. Which of the following outcomes is most likely to result from this decision?

Accepted Answer

Increased negative predictive value

Answer

Unchanged true positive results

Answer

Decreased sensitivity

Answer

Increased specificity

Answer

Increased positive predictive value

Question 2

A 23-year-old woman with no significant past medical history currently on oral contraceptive pills presents to the emergency department with pleuritic chest pain. She states that it started today. Yesterday she had a trip and returned via plane. Her temperature is 98°F (36.7°C), blood pressure is 117/66 mmHg, pulse is 105/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical exam reveals tachycardia, a normal S1 and S2, and clear breath sounds. The patient’s lower extremities are non-tender and symmetric. Chest pain is not reproducible with position changes or palpation but is worsened with deep breaths. Which of the following is the most appropriate next test for this patient?

Accepted Answer

CT angiogram

Answer

D-dimer

Answer

Ultrasound of the lower extremities

Answer

Ventilation-perfusion scan

Answer

Chest radiograph

Question 3

A scientist in Boston is studying a new blood test to detect Ab to the parainfluenza virus with increased sensitivity and specificity. So far, her best attempt at creating such an exam reached 82% sensitivity and 88% specificity. She is hoping to increase these numbers by at least 2 percent for each value. After several years of work, she believes that she has actually managed to reach a sensitivity and specificity even greater than what she had originally hoped for. She travels to South America to begin testing her newest blood test. She finds 2,000 patients who are willing to participate in her study. Of the 2,000 patients, 1,200 of them are known to be infected with the parainfluenza virus. The scientist tests these 1,200 patients’ blood and finds that only 120 of them tested negative with her new test. Of the following options, which describes the sensitivity of the test?

Accepted Answer

90%

Answer

82%

Answer

86%

Answer

98%

Answer

84%

Question 4

A geriatric investigator is evaluating the consistency of Alzheimer dementia diagnoses based on clinical symptoms. Patients with known chart diagnoses of Alzheimer dementia were evaluated by multiple physicians during a fixed time interval. Each evaluator was blinded to the others' assessments. The extent to which the diagnosis by one physician was replicated by another clinician examining the same patient is best described by which of the following terms?

Accepted Answer

Precision

Answer

Validity

Answer

Specificity

Answer

Predictive value

Answer

Sensitivity

Question 5

A research group wants to assess the safety and toxicity profile of a new drug. A clinical trial is conducted with 20 volunteers to estimate the maximum tolerated dose and monitor the apparent toxicity of the drug. The study design is best described as which of the following phases of a clinical trial?

Accepted Answer

Phase I

Answer

Phase 0

Answer

Phase III

Answer

Phase V

Answer

Phase II

Question 6

A pharmaceutical corporation is developing a research study to evaluate a novel blood test to screen for breast cancer. They enrolled 800 patients in the study, half of which have breast cancer. The remaining enrolled patients are age-matched controls who do not have the disease. Of those in the diseased arm, 330 are found positive for the test. Of the patients in the control arm, only 30 are found positive. What is this test’s sensitivity?

Accepted Answer

330 / (330 + 70)

Answer

330 / (330 + 30)

Answer

370 / (30 + 370)

Answer

370 / (70 + 370)

Answer

330 / (400 + 400)

Question 7

Three days after undergoing laparoscopic colectomy, a 67-year-old man reports swelling and pain in his right leg. He was diagnosed with colon cancer 1 month ago. His temperature is 38.5°C (101.3°F). Physical examination shows swelling of the right leg from the ankle to the thigh. There is no erythema or rash. Which of the following is likely to be most helpful in establishing the diagnosis?

Accepted Answer

Compression ultrasonography

Answer

D-dimer level

Answer

CT pulmonary angiography

Answer

Transthoracic echocardiography

Answer

Blood cultures

Question 8

A medical research study is beginning to evaluate the positive predictive value of a novel blood test for non-Hodgkin’s lymphoma. The diagnostic arm contains 700 patients with NHL, of which 400 tested positive for the novel blood test. In the control arm, 700 age-matched control patients are enrolled and 0 are found positive for the novel test. What is the PPV of this test?

Accepted Answer

400 / (400 + 0)

Answer

700 / (700 + 300)

Answer

400 / (400 + 300)

Answer

700 / (700 + 0)

Answer

700 / (400 + 400)

Question 9

In recent years, psoriasis has been identified as a risk factor for cardiovascular disease. A researcher conducted a study in which he identified 200 patients with psoriasis and 200 patients without psoriasis. The patients were followed for 10 years. At the end of this period, participants' charts were reviewed for myocardial infarction during this time interval.
Myocardial infarction No myocardial infarction Total
Psoriasis 12 188 200
No psoriasis 4 196 200
Total 16 384 400
What is the 10-year risk of myocardial infarction in participants with psoriasis?

Accepted Answer

0.06

Answer

0.75

Answer

0.04

Answer

0.5

Answer

0.02

Question 10

A population is studied for risk factors associated with testicular cancer. Alcohol exposure, smoking, dietary factors, social support, and environmental exposure are all assessed. The researchers are interested in the incidence and prevalence of the disease in addition to other outcomes. Which pair of studies would best assess the 1. incidence and 2. prevalence?

Accepted Answer

1. Prospective cohort study 2. Cross sectional study

Answer

1. Prospective cohort study 2. Retrospective cohort study

Answer

1. Cross sectional study 2. Retrospective cohort study

Answer

1. Case-control study 2. Prospective cohort study

Answer

1. Clinical trial 2. Cross sectional study

Sensitivity/Specificity

Study Resources

Lessons

Questions

Flashcards

Lessons

Definitions and calculations

2x2 contingency tables

Relationship with false positive/negative rates

Positive predictive value (PPV)

Negative predictive value (NPV)

Effect of disease prevalence on predictive values

Likelihood ratios

ROC curve analysis

Area under the curve (AUC) interpretation

Optimizing cut-off values

Trade-offs between sensitivity and specificity

Multi-test algorithms

Application to screening programs

Practice Questions

Flashcards

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