Sensitivity/Specificity Practice Questions

Question 1

A scientist in Chicago is studying a new blood test to detect Ab to EBV 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 much greater than what she had originally hoped for. She travels to China 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 EBV. The scientist tests these 1,200 patients' blood and finds that only 120 of them tested negative with her new exam. Of the patients who are known to be EBV-free, only 20 of them tested positive. Given these results, which of the following correlates with the exam's specificity?

Accepted Answer

98%

Answer

82%

Answer

90%

Answer

84%

Answer

86%

Question 2

A researcher is trying to determine whether a newly discovered substance X can be useful in promoting wound healing after surgery. She conducts this study by enrolling the next 100 patients that will be undergoing this surgery and separating them into 2 groups. She decides which patient will be in which group by using a random number generator. Subsequently, she prepares 1 set of syringes with the novel substance X and 1 set of syringes with a saline control. Both of these sets of syringes are unlabeled and the substances inside cannot be distinguished. She gives the surgeon performing the surgery 1 of the syringes and does not inform him nor the patient which syringe was used. After the study is complete, she analyzes all the data that was collected and performs statistical analysis. This study most likely provides which level of evidence for use of substance X?

Accepted Answer

Level 1

Answer

Level 3

Answer

Level 4

Answer

Level 5

Answer

Level 2

Question 3

You conduct a medical research study to determine the screening efficacy of a novel serum marker for colon cancer. The study is divided into 2 subsets. In the first, there are 500 patients with colon cancer, of which 450 are found positive for the novel serum marker. In the second arm, there are 500 patients who do not have colon cancer, and only 10 are found positive for the novel serum marker. What is the overall sensitivity of this novel test?

Accepted Answer

450 / (450 + 50)

Answer

450 / (450 + 10)

Answer

490 / (10 + 490)

Answer

490 / (50 + 490)

Answer

490 / (450 + 490)

Question 4

A 25-year-old man comes to the physician for severe back pain. He describes the pain as shooting and stabbing. On a 10-point scale, he rates the pain as a 9 to 10. The pain started after he lifted a heavy box at work; he works at a supermarket and recently switched from being a cashier to a storekeeper. The patient appears to be in severe distress. Vital signs are within normal limits. On physical examination, the spine is nontender without paravertebral muscle spasms. Range of motion is normal. A straight-leg raise test is negative. After the physical examination has been completed, the patient asks for a letter to his employer attesting to his inability to work as a storekeeper. Which of the following is the most appropriate response?

Accepted Answer

I understand that you are uncomfortable, but the findings do not match the severity of your symptoms. Let's talk about the recent changes at your job.

Answer

“Yes. Since work may worsen your condition, I would prefer that you stay home a few days. I will write a letter to your employer to explain the situation.”

Answer

You say you are in severe pain. However, the physical examination findings do not suggest a physical problem that can be addressed with medications or surgery. I'd like to meet on a regular basis to see how you're doing.

Answer

The physical exam findings do not match your symptoms, which suggests a psychological problem. I would be happy to refer you to a mental health professional.

Answer

The physical exam findings suggest a psychological rather than a physical problem. But there is a good chance that we can address it with cognitive-behavioral therapy.

Question 5

The World Health Organization suggests the use of a new rapid diagnostic test for the diagnosis of malaria in resource-limited settings. The new test has a sensitivity of 70% and a specificity of 90% compared to the gold standard test (blood smear). The validity of the new test is evaluated at a satellite health center by testing 200 patients with a positive blood smear and 150 patients with a negative blood smear. How many of the tested individuals are expected to have a false negative result?

Accepted Answer

60

Answer

15

Answer

135

Answer

155

Answer

195

Question 6

During an evaluation of a new diagnostic imaging modality for detecting salivary gland tumors, 90 patients tested positive out of the 100 patients who tested positive with the gold standard test. A total of 80 individuals tested negative with the new test out of the 100 individuals who tested negative with the gold standard test. What is the positive likelihood ratio for this test?

Accepted Answer

90/20

Answer

80/90

Answer

90/100

Answer

90/110

Answer

10/80

Question 7

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

Accepted Answer

"Can you tell me more about the symptoms you have been experiencing?"

Answer

"Does the diarrhea typically precede the constipation, or vice-versa?"

Answer

"Is the diarrhea foul-smelling?"

Answer

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

Answer

"Are the symptoms worse in the morning or at night?"

Question 8

A 65-year-old man is admitted to the hospital because of a 1-month history of fatigue, intermittent fever, and weakness. Results from a peripheral blood smear taken during his evaluation are indicative of possible acute myeloid leukemia. Bone marrow aspiration and subsequent cytogenetic studies confirm the diagnosis. The physician sets aside an appointed time-slot and arranges a meeting in a quiet office to inform him about the diagnosis and discuss his options. He has been encouraged to bring someone along to the appointment if he wanted. He comes to your office at the appointed time with his daughter. He appears relaxed, with a full range of affect. Which of the following is the most appropriate opening statement in this situation?

Accepted Answer

What is your understanding of the reasons we did bone marrow aspiration and cytogenetic studies?

Answer

Your lab reports show that you have an acute myeloid leukemia

Answer

You must be curious and maybe even anxious about the results of your tests.

Answer

I may need to refer you to a blood cancer specialist because of your diagnosis. You may need chemotherapy or radiotherapy, which we are not equipped for.

Answer

Would you like to know all the details of your diagnosis, or would you prefer I just explain to you what our options are?

Question 9

A 3-year-old child is brought to the pediatrician by his mother who states that he has been fussy for the past two days. She says that he has had a runny nose, a cough, a sore throat, and decreased appetite. Vital signs are within normal limits. Physical exam reveals a slightly erythematous oropharynx and clear nasal discharge. The mother states that she is a single mother working at a busy law firm. The mother demands that the child receive antibiotics, as her babysitter refuses to care for the child unless he is treated with antibiotics. You diagnose the child with the common cold and inform the mother that antibiotics are not indicated. She is infuriated and accuses you of refusing to treat her child appropriately. How should you respond?

Accepted Answer

Explain the reasoning as to why antibiotics are not indicated for the common cold

Answer

Prescribe a placebo

Answer

Ask the mother to leave immediately

Answer

Prescribe antibiotics to the child

Answer

Refer the mother to a nearby physician who will prescribe antibiotics

Question 10

A 45-year-old man presents for his annual checkup. The patient has a past medical history of diabetes mellitus (DM) type 2 that is well-controlled with diet. In addition, he was admitted to this hospital 1-year ago for a myocardial infarction (MI). The patient reports a 40-pack-year smoking history. However, after his MI, his doctors informed him about how detrimental smoking was to his heart condition. Since then, he has made efforts to cut down and now, for the past seven months, has stopped smoking. He says he used to use smoking as a means of dealing with his work and family stresses. He now attends wellness sessions at work and meditates early every morning before the family wakes up. Which of the following stages of the transtheoretical model is this patient most likely in?

Accepted Answer

Maintenance

Answer

Preparation

Answer

Contemplation

Answer

Action

Answer

Precontemplation

Sensitivity/Specificity

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Test characteristics fundamentals

Sensitivity calculation and interpretation

Specificity calculation and interpretation

Positive predictive value

Negative predictive value

Prevalence effects on predictive values

ROC curves

Likelihood ratios

Bayes theorem application

Screening test selection criteria

Diagnostic thresholds

Serial vs parallel testing

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