Group of 100 medical students took an end of the year exam. The mean score on the exam was 70%, with a standard deviation of 25%. The professor states that a student's score must be within the 95% confidence interval of the mean to pass the exam. Which of the following is the minimum score a student can have to pass the exam?
Q2
A research team develops a new monoclonal antibody checkpoint inhibitor for advanced melanoma that has shown promise in animal studies as well as high efficacy and low toxicity in early phase human clinical trials. The research team would now like to compare this drug to existing standard of care immunotherapy for advanced melanoma. The research team decides to conduct a non-randomized study where the novel drug will be offered to patients who are deemed to be at risk for toxicity with the current standard of care immunotherapy, while patients without such risk factors will receive the standard treatment. Which of the following best describes the level of evidence that this study can offer?
Q3
A researcher is conducting a study to compare fracture risk in male patients above the age of 65 who received annual DEXA screening to peers who did not receive screening. He conducts a randomized controlled trial in 900 patients, with half of participants assigned to each experimental group. The researcher ultimately finds similar rates of fractures in the two groups. He then notices that he had forgotten to include 400 patients in his analysis. Including the additional participants in his analysis would most likely affect the study's results in which of the following ways?
Q4
A 57-year-old man presents to the clinic for a chronic cough over the past 4 months. The patient reports a productive yellow/green cough that is worse at night. He denies any significant precipitating event prior to his symptoms. He denies fever, chest pain, palpitations, weight changes, or abdominal pain, but endorses some difficulty breathing that waxes and wanes. He denies alcohol usage but endorses a 35 pack-year smoking history. A physical examination demonstrates mild wheezes, bibasilar crackles, and mild clubbing of his fingertips. A pulmonary function test is subsequently ordered, and partial results are shown below:
Tidal volume: 500 mL
Residual volume: 1700 mL
Expiratory reserve volume: 1500 mL
Inspiratory reserve volume: 3000 mL
What is the functional residual capacity of this patient?
Q5
A student health coordinator plans on leading a campus-wide HIV screening program that will be free for the entire undergraduate student body. The goal is to capture as many correct HIV diagnoses as possible with the fewest false positives. The coordinator consults with the hospital to see which tests are available to use for this program. Test A has a sensitivity of 0.92 and a specificity of 0.99. Test B has a sensitivity of 0.95 and a specificity of 0.96. Test C has a sensitivity of 0.98 and a specificity of 0.93. Which of the following testing schemes should the coordinator pursue?
Q6
A 21-year-old U.S. born first year medical student with no prior hospital or healthcare work presents to the physician for a routine physical exam. The patient is HIV negative, denies drug use, and denies sick contacts. The physician places a purified protein tuberculin test in the patient's right forearm intradermally. What is the proper time to read the test and induration diameter that would indicate a positive test result?
Q7
A 26-year-old female medical student presents to occupational health after sustaining a needlestick injury. She reports that she was drawing blood from an HIV-positive patient when she stuck herself percutaneously while capping the needle. She immediately washed the puncture wound with betadine. The medical student has a negative HIV serology from the beginning of medical school two years ago. She is monogamous with one male partner and denies any intravenous drug use. The source patient was recently diagnosed with HIV, and has a CD4 count of 550 cells/µL. His most recent viral load is 1,800,000 copies/mL, and he was started on HAART three days ago.
Which of the following is the best next step to manage the female medical student’s exposure?
Q8
A regional academic medical center has 10 cases of adenovirus in the span of a week among its ICU patients. A committee is formed to investigate this outbreak. They are tasked with identifying the patients and interviewing the care providers to understand how adenovirus could have been spread from patient to patient. This committee will review charts, talk to the care provider teams, and investigate current patient safety and sanitation measures in the ICU. The goal of the committee is to identify weaknesses in the current system and to put in place a plan to help prevent this sort of outbreak from reoccurring in the future. The committee is most likely using what type of analysis?
Review and reflection strategies US Medical PG Practice Questions and MCQs
Question 1: Group of 100 medical students took an end of the year exam. The mean score on the exam was 70%, with a standard deviation of 25%. The professor states that a student's score must be within the 95% confidence interval of the mean to pass the exam. Which of the following is the minimum score a student can have to pass the exam?
A. 45%
B. 63.75%
C. 67.5%
D. 20%
E. 65% (Correct Answer)
Explanation: ***65%***
- To find the **95% confidence interval (CI) of the mean**, we use the formula: Mean ± (Z-score × Standard Error). For a 95% CI, the Z-score is approximately **1.96**.
- The **Standard Error (SE)** is calculated as SD/√n, where n is the sample size (100 students). So, SE = 25%/√100 = 25%/10 = **2.5%**.
- The 95% CI is 70% ± (1.96 × 2.5%) = 70% ± 4.9%. The lower bound is 70% - 4.9% = **65.1%**, which rounds to **65%** as the minimum passing score.
*45%*
- This value is significantly lower than the calculated lower bound of the 95% confidence interval (approximately 65.1%).
- It would represent a score far outside the defined passing range.
*63.75%*
- This value falls below the calculated lower bound of the 95% confidence interval (approximately 65.1%).
- While close, this score would not meet the professor's criterion for passing.
*67.5%*
- This value is within the 95% confidence interval (65.1% to 74.9%) but is **not the minimum score**.
- Lower scores within the interval would still qualify as passing.
*20%*
- This score is extremely low and falls significantly outside the 95% confidence interval for a mean of 70%.
- It would indicate performance far below the defined passing threshold.
Question 2: A research team develops a new monoclonal antibody checkpoint inhibitor for advanced melanoma that has shown promise in animal studies as well as high efficacy and low toxicity in early phase human clinical trials. The research team would now like to compare this drug to existing standard of care immunotherapy for advanced melanoma. The research team decides to conduct a non-randomized study where the novel drug will be offered to patients who are deemed to be at risk for toxicity with the current standard of care immunotherapy, while patients without such risk factors will receive the standard treatment. Which of the following best describes the level of evidence that this study can offer?
A. Level 1
B. Level 3 (Correct Answer)
C. Level 5
D. Level 4
E. Level 2
Explanation: ***Level 3***
- A **non-randomized controlled trial** like the one described, where patient assignment to treatment groups is based on specific characteristics (risk of toxicity), falls into Level 3 evidence.
- This level typically includes **non-randomized controlled trials** and **well-designed cohort studies** with comparison groups, which are prone to selection bias and confounding.
- The study compares two treatments but lacks randomization, making it Level 3 evidence.
*Level 1*
- Level 1 evidence is the **highest level of evidence**, derived from **systematic reviews and meta-analyses** of multiple well-designed randomized controlled trials or large, high-quality randomized controlled trials.
- The described study is explicitly stated as non-randomized, ruling out Level 1.
*Level 2*
- Level 2 evidence involves at least one **well-designed randomized controlled trial** (RCT) or **systematic reviews** of randomized trials.
- The current study is *non-randomized*, which means it cannot be classified as Level 2 evidence, as randomization is a key criterion for this level.
*Level 4*
- Level 4 evidence includes **case series**, **case-control studies**, and **poorly designed cohort or case-control studies**.
- While the study is non-randomized, it is a controlled comparative trial rather than a case series or retrospective case-control study, placing it at Level 3.
*Level 5*
- Level 5 evidence is the **lowest level of evidence**, typically consisting of **expert opinion** without explicit critical appraisal, or based on physiology, bench research, or animal studies.
- While the drug was initially tested in animal studies, the current human comparative study offers a higher level of evidence than expert opinion or preclinical data.
Question 3: A researcher is conducting a study to compare fracture risk in male patients above the age of 65 who received annual DEXA screening to peers who did not receive screening. He conducts a randomized controlled trial in 900 patients, with half of participants assigned to each experimental group. The researcher ultimately finds similar rates of fractures in the two groups. He then notices that he had forgotten to include 400 patients in his analysis. Including the additional participants in his analysis would most likely affect the study's results in which of the following ways?
A. Wider confidence intervals of results
B. Increased probability of committing a type II error
C. Decreased significance level of results
D. Increased external validity of results
E. Increased probability of rejecting the null hypothesis when it is truly false (Correct Answer)
Explanation: ***Increased probability of rejecting the null hypothesis when it is truly false***
- Including more participants increases the **statistical power** of the study, making it more likely to detect a true effect if one exists.
- A higher sample size provides a more precise estimate of the population parameters, leading to a greater ability to **reject a false null hypothesis**.
*Wider confidence intervals of results*
- A larger sample size generally leads to **narrower confidence intervals**, as it reduces the standard error of the estimate.
- Narrower confidence intervals indicate **greater precision** in the estimation of the true population parameter.
*Increased probability of committing a type II error*
- A **Type II error** (false negative) occurs when a study fails to reject a false null hypothesis.
- Increasing the sample size typically **reduces the probability of a Type II error** because it increases statistical power.
*Decreased significance level of results*
- The **significance level (alpha)** is a pre-determined threshold set by the researcher before the study begins, typically 0.05.
- It is independent of sample size and represents the **acceptable probability of committing a Type I error** (false positive).
*Increased external validity of results*
- **External validity** refers to the generalizability of findings to other populations, settings, or times.
- While a larger sample size can enhance the representativeness of the study population, external validity is primarily determined by the **sampling method** and the study's design context, not just sample size alone.
Question 4: A 57-year-old man presents to the clinic for a chronic cough over the past 4 months. The patient reports a productive yellow/green cough that is worse at night. He denies any significant precipitating event prior to his symptoms. He denies fever, chest pain, palpitations, weight changes, or abdominal pain, but endorses some difficulty breathing that waxes and wanes. He denies alcohol usage but endorses a 35 pack-year smoking history. A physical examination demonstrates mild wheezes, bibasilar crackles, and mild clubbing of his fingertips. A pulmonary function test is subsequently ordered, and partial results are shown below:
Tidal volume: 500 mL
Residual volume: 1700 mL
Expiratory reserve volume: 1500 mL
Inspiratory reserve volume: 3000 mL
What is the functional residual capacity of this patient?
A. 4500 mL
B. 2000 mL
C. 2200 mL
D. 3200 mL (Correct Answer)
E. 3500 mL
Explanation: ***3200 mL***
- The **functional residual capacity (FRC)** is the volume of air remaining in the lungs after a normal expiration.
- It is calculated as the sum of the **expiratory reserve volume (ERV)** and the **residual volume (RV)**. In this case, 1500 mL (ERV) + 1700 mL (RV) = 3200 mL.
*4500 mL*
- This value represents the sum of the **inspiratory reserve volume (3000 mL)** and the **residual volume (1700 mL)**, which does not correspond to a standard lung volume or capacity.
- It does not logically relate to the definition of functional residual capacity.
*2000 mL*
- This value represents the sum of the **tidal volume (500 mL)** and the **expiratory reserve volume (1500 mL)**, which is incorrect for FRC.
- This would represent the inspiratory capacity minus the inspiratory reserve volume, which is not a standard measurement used in pulmonary function testing.
*2200 mL*
- This value could be obtained by incorrectly adding the **tidal volume (500 mL)** and the **residual volume (1700 mL)**, which is not the correct formula for FRC.
- This calculation represents a miscombination of lung volumes that does not correspond to any standard pulmonary capacity measurement.
*3500 mL*
- This value is the sum of the **tidal volume (500 mL)**, the **expiratory reserve volume (1500 mL)**, and the **residual volume (1700 mL)**.
- This would represent the FRC plus the tidal volume, which is not a standard measurement and does not represent the functional residual capacity.
Question 5: A student health coordinator plans on leading a campus-wide HIV screening program that will be free for the entire undergraduate student body. The goal is to capture as many correct HIV diagnoses as possible with the fewest false positives. The coordinator consults with the hospital to see which tests are available to use for this program. Test A has a sensitivity of 0.92 and a specificity of 0.99. Test B has a sensitivity of 0.95 and a specificity of 0.96. Test C has a sensitivity of 0.98 and a specificity of 0.93. Which of the following testing schemes should the coordinator pursue?
A. Test A on the entire student body followed by Test B on those who are positive
B. Test A on the entire student body followed by Test C on those who are positive
C. Test C on the entire student body followed by Test B on those who are positive
D. Test C on the entire student body followed by Test A on those who are positive (Correct Answer)
E. Test B on the entire student body followed by Test A on those who are positive
Explanation: ***Test C on the entire student body followed by Test A on those who are positive***
- To "capture as many correct HIV diagnoses as possible" (maximize true positives), the initial screening test should have the **highest sensitivity**. Test C has the highest sensitivity (0.98).
- To "capture as few false positives as possible" (maximize true negatives and confirm diagnoses), the confirmatory test should have the **highest specificity**. Test A has the highest specificity (0.99).
*Test A on the entire student body followed by Test B on those who are positive*
- Starting with Test A (sensitivity 0.92) would miss more true positive cases than starting with Test C (sensitivity 0.98), failing the goal of **capturing as many cases as possible**.
- Following with Test B (specificity 0.96) would result in more false positives than following with Test A (specificity 0.99).
*Test A on the entire student body followed by Test C on those who are positive*
- This scheme would miss many true positive cases initially due to Test A's lower sensitivity compared to Test C.
- Following with Test C would introduce more false positives than necessary, as it has a lower specificity (0.93) than Test A (0.99).
*Test C on the entire student body followed by Test B on those who are positive*
- While Test C is a good initial screen for its high sensitivity, following it with Test B (specificity 0.96) is less optimal than Test A (specificity 0.99) for minimizing false positives in the confirmation step.
- This combination would therefore yield more false positives in the confirmatory stage than using Test A.
*Test B on the entire student body followed by Test A on those who are positive*
- Test B has a sensitivity of 0.95, which is lower than Test C's sensitivity of 0.98, meaning it would miss more true positive cases at the initial screening stage.
- While Test A provides excellent specificity for confirmation, the initial screening step is suboptimal for the goal of capturing as many diagnoses as possible.
Question 6: A 21-year-old U.S. born first year medical student with no prior hospital or healthcare work presents to the physician for a routine physical exam. The patient is HIV negative, denies drug use, and denies sick contacts. The physician places a purified protein tuberculin test in the patient's right forearm intradermally. What is the proper time to read the test and induration diameter that would indicate a positive test result?
A. 36 hours and 7mm diameter
B. 48 hours and 11mm diameter
C. 72 hours and 16mm diameter (Correct Answer)
D. 96 hours and 14mm diameter
E. 24 hours and 18mm diameter
Explanation: ***72 hours and 16mm diameter***
- The **purified protein derivative (PPD) test** should ideally be read between 48 and 72 hours after administration to allow for the **Type IV hypersensitivity reaction** to fully develop.
- For individuals with no known risk factors for tuberculosis and no prior exposure, an induration of **≥15 mm** is considered a positive result. A 16mm diameter falls within this range.
*36 hours and 7mm diameter*
- **36 hours** is too early to accurately read a PPD test, as the delayed-type hypersensitivity reaction may not have fully manifested.
- A **7mm induration** would generally be considered negative in a low-risk individual, as the threshold for positivity in this group is higher.
*48 hours and 11mm diameter*
- While **48 hours** is within the acceptable window for reading a PPD test, an **11mm induration** is not considered positive for a young, low-risk individual without any predisposing conditions like HIV or organ transplant.
- The threshold for a positive result in this demographic is typically **≥15 mm**.
*96 hours and 14mm diameter*
- **96 hours** (4 days) is generally too late to accurately read a PPD test, as the reaction may begin to fade, leading to a potentially false negative.
- A **14mm induration** is still below the positive threshold of ≥15mm for a low-risk individual.
*24 hours and 18mm diameter*
- **24 hours** is significantly too early to read a PPD test, as the immune response will not have fully developed, leading to unreliable results.
- While **18mm induration** would be a positive result, the timing makes the reading invalid.
Question 7: A 26-year-old female medical student presents to occupational health after sustaining a needlestick injury. She reports that she was drawing blood from an HIV-positive patient when she stuck herself percutaneously while capping the needle. She immediately washed the puncture wound with betadine. The medical student has a negative HIV serology from the beginning of medical school two years ago. She is monogamous with one male partner and denies any intravenous drug use. The source patient was recently diagnosed with HIV, and has a CD4 count of 550 cells/µL. His most recent viral load is 1,800,000 copies/mL, and he was started on HAART three days ago.
Which of the following is the best next step to manage the female medical student’s exposure?
A. Draw her repeat HIV serology and initiate three-drug antiretroviral therapy if positive
B. Perform genotype testing on source patient and initiate antiretroviral therapy tailored to results
C. Immediately initiate three-drug antiretroviral therapy
D. Draw her repeat HIV serology and immediately initiate three-drug antiretroviral therapy (Correct Answer)
E. Draw her repeat HIV serology and initiate three-drug antiretroviral therapy if negative
Explanation: ***Draw her repeat HIV serology and immediately initiate three-drug antiretroviral therapy***
- This approach ensures that baseline **HIV status** is established while simultaneously providing **post-exposure prophylaxis (PEP)** as quickly as possible. Time is critical for PEP efficacy.
- The patient has a high-risk exposure (percutaneous injury, high viral load source) warranting immediate initiation of a **three-drug antiretroviral regimen** to prevent seroconversion.
*Draw her repeat HIV serology and initiate three-drug antiretroviral therapy if positive*
- Waiting for serology results before initiating therapy would delay PEP, significantly reducing its effectiveness in potentially preventing **HIV transmission**.
- If the student is already HIV-positive from a prior undisclosed exposure, PEP for a new exposure is not the primary concern; rather, she would need full **HIV treatment**. However, the immediate concern after an exposure is always prevention.
*Immediately initiate three-drug antiretroviral therapy*
- While immediate initiation of PEP is correct, it is still crucial to obtain a **baseline HIV serology** for the exposed individual.
- This baseline allows for clear documentation of the pre-exposure HIV status, which is vital for any future testing and counseling following the exposure.
*Draw her repeat HIV serology and initiate three-drug antiretroviral therapy if negative*
- Waiting for serology results to return before starting PEP is incorrect as this would significantly delay the initiation of therapy.
- The critical window for effective PEP is within hours of exposure, ideally within 72 hours.
*Perform genotype testing on source patient and initiate antiretroviral therapy tailored to results*
- While **genotype testing** on the source patient provides valuable information about drug resistance, it should not delay the immediate initiation of **empiric PEP** for the exposed individual.
- PEP must be started as soon as possible, and the regimen can be adjusted later if the genotype results indicate resistance to the initial drugs.
Question 8: A regional academic medical center has 10 cases of adenovirus in the span of a week among its ICU patients. A committee is formed to investigate this outbreak. They are tasked with identifying the patients and interviewing the care providers to understand how adenovirus could have been spread from patient to patient. This committee will review charts, talk to the care provider teams, and investigate current patient safety and sanitation measures in the ICU. The goal of the committee is to identify weaknesses in the current system and to put in place a plan to help prevent this sort of outbreak from reoccurring in the future. The committee is most likely using what type of analysis?
A. Simulation
B. Root cause analysis (Correct Answer)
C. Algorithmic analysis
D. Heuristic analysis
E. Failure mode and effects analysis
Explanation: ***Root cause analysis***
- The committee's goal is to **identify weaknesses** in the current system and **prevent recurrence**, which aligns perfectly with the principles of **root cause analysis (RCA)**.
- RCA is a structured method for **identifying the underlying causes** of problems or incidents, rather than just addressing symptoms.
*Simulation*
- **Simulation** involves creating a model of a process or system to test different scenarios and predict outcomes.
- While useful for planning, it's not the primary method for investigating an actual past event or identifying causative factors after an outbreak has occurred.
*Algorithmic analysis*
- **Algorithmic analysis** is primarily used in computer science to evaluate the efficiency and complexity of algorithms.
- It does not apply to investigating the spread of infectious diseases or healthcare system failures.
*Heuristic analysis*
- **Heuristic analysis** involves using a rule of thumb or an educated guess to solve a problem quickly and efficiently, especially when perfect solutions are not feasible.
- This approach is less systematic and comprehensive than what is required to thoroughly investigate an outbreak and identify root causes.
*Failure mode and effects analysis*
- **Failure mode and effects analysis (FMEA)** is a proactive method used to identify **potential failure modes** in a system and their effects *before* an event occurs.
- The committee is investigating an **already existing problem**, making RCA more appropriate than FMEA, which is used for risk assessment of future processes.
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