NNT in prevention vs treatment US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for NNT in prevention vs treatment. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
NNT in prevention vs treatment US Medical PG Question 1: You are conducting a study comparing the efficacy of two different statin medications. Two groups are placed on different statin medications, statin A and statin B. Baseline LDL levels are drawn for each group and are subsequently measured every 3 months for 1 year. Average baseline LDL levels for each group were identical. The group receiving statin A exhibited an 11 mg/dL greater reduction in LDL in comparison to the statin B group. Your statistical analysis reports a p-value of 0.052. Which of the following best describes the meaning of this p-value?
- A. There is a 95% chance that the difference in reduction of LDL observed reflects a real difference between the two groups
- B. Though A is more effective than B, there is a 5% chance the difference in reduction of LDL between the two groups is due to chance
- C. If 100 permutations of this experiment were conducted, 5 of them would show similar results to those described above
- D. This is a statistically significant result
- E. There is a 5.2% chance of observing a difference in reduction of LDL of 11 mg/dL or greater even if the two medications have identical effects (Correct Answer)
NNT in prevention vs treatment Explanation: **There is a 5.2% chance of observing a difference in reduction of LDL of 11 mg/dL or greater even if the two medications have identical effects**
- The **p-value** represents the probability of observing results as extreme as, or more extreme than, the observed data, assuming the **null hypothesis** is true (i.e., there is no true difference between the groups).
- A p-value of 0.052 means there's approximately a **5.2% chance** that the observed 11 mg/dL difference (or a more substantial difference) occurred due to **random variation**, even if both statins were equally effective.
*There is a 95% chance that the difference in reduction of LDL observed reflects a real difference between the two groups*
- This statement is an incorrect interpretation of the p-value; it confuses the p-value with the **probability that the alternative hypothesis is true**.
- A p-value does not directly tell us the probability that the observed difference is "real" or due to the intervention being studied.
*Though A is more effective than B, there is a 5% chance the difference in reduction of LDL between the two groups is due to chance*
- This statement implies that Statin A is more effective, which cannot be concluded with a p-value of 0.052 if the significance level (alpha) was set at 0.05.
- While it's true there's a chance the difference is due to chance, claiming A is "more effective" based on this p-value before statistical significance is usually declared is misleading.
*If 100 permutations of this experiment were conducted, 5 of them would show similar results to those described above*
- This is an incorrect interpretation. The p-value does not predict the outcome of repeated experiments in this manner.
- It refers to the **probability under the null hypothesis in a single experiment**, not the frequency of results across multiple hypothetical repetitions.
*This is a statistically significant result*
- A p-value of 0.052 is generally considered **not statistically significant** if the conventional alpha level (significance level) is set at 0.05 (or 5%).
- For a result to be statistically significant at alpha = 0.05, the p-value must be **less than 0.05**.
NNT in prevention vs treatment US Medical PG Question 2: A 25-year-old man with a genetic disorder presents for genetic counseling because he is concerned about the risk that any children he has will have the same disease as himself. Specifically, since childhood he has had difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy. He has also had diarrhea and malabsorption requiring enzyme replacement therapy. If his wife comes from a population where 1 in 10,000 people are affected by this same disorder, which of the following best represents the likelihood a child would be affected as well?
- A. 0.01%
- B. 2%
- C. 0.5%
- D. 1% (Correct Answer)
- E. 50%
NNT in prevention vs treatment Explanation: ***Correct Option: 1%***
- The patient's symptoms (difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy; diarrhea and malabsorption requiring enzyme replacement therapy) are classic for **cystic fibrosis (CF)**, an **autosomal recessive disorder**.
- For an autosomal recessive disorder with a prevalence of 1 in 10,000 in the general population, **q² = 1/10,000**, so **q = 1/100 = 0.01**. The carrier frequency **(2pq)** is approximately **2q = 2 × (1/100) = 1/50 = 0.02**.
- The affected man is **homozygous recessive (aa)** and will always pass on the recessive allele. His wife has a **1/50 chance of being a carrier (Aa)**. If she is a carrier, she has a **1/2 chance of passing on the recessive allele**.
- Therefore, the probability of an affected child = **(Probability wife is a carrier) × (Probability wife passes recessive allele) = 1/50 × 1/2 = 1/100 = 1%**.
*Incorrect Option: 0.01%*
- This percentage is too low and does not correctly account for the carrier frequency in the population and the probability of transmission from a carrier mother.
*Incorrect Option: 2%*
- This represents approximately the carrier frequency (1/50 ≈ 2%), but does not account for the additional 1/2 probability that a carrier mother would pass on the recessive allele.
*Incorrect Option: 0.5%*
- This value would be correct if the carrier frequency were 1/100 instead of 1/50, which does not match the given population prevalence.
*Incorrect Option: 50%*
- **50%** would be the risk if both parents were carriers of an autosomal recessive disorder (1/4 chance = 25% for affected, but if we know one parent passes the allele, conditional probability changes). More accurately, 50% would apply if the disorder were **autosomal dominant** with one affected parent, which is not the case here.
NNT in prevention vs treatment US Medical PG 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?
- A. 450 / (450 + 10)
- B. 490 / (10 + 490)
- C. 490 / (50 + 490)
- D. 450 / (450 + 50) (Correct Answer)
- E. 490 / (450 + 490)
NNT in prevention vs treatment Explanation: ***450 / (450 + 50)***
- **Sensitivity** is defined as the proportion of actual positive cases that are correctly identified by the test.
- In this study, there are **500 patients with colon cancer** (actual positives), and **450 of them tested positive** for the marker, while **50 tested negative** (500 - 450 = 50). Therefore, sensitivity = 450 / (450 + 50) = 450/500 = 0.9 or 90%.
*450 / (450 + 10)*
- This formula represents **Positive Predictive Value (PPV)**, which is the probability that a person with a positive test result actually has the disease.
- It incorrectly uses the total number of **test positives** in the denominator (450 true positives + 10 false positives) instead of the total number of diseased individuals, which is needed for sensitivity.
*490 / (10 + 490)*
- This is actually the correct formula for **specificity**, not sensitivity.
- Specificity = TN / (FP + TN) = 490 / (10 + 490) = 490/500 = 0.98 or 98%, which measures the proportion of actual negative cases correctly identified.
- The question asks for sensitivity, not specificity.
*490 / (50 + 490)*
- This formula incorrectly mixes **true negatives (490)** with **false negatives (50)** in an attempt to calculate specificity.
- The correct specificity formula should use false positives (10), not false negatives (50), in the denominator: 490 / (10 + 490).
*490 / (450 + 490)*
- This calculation incorrectly combines **true negatives (490)** and **true positives (450)** in the denominator, which does not correspond to any standard epidemiological measure.
- Neither sensitivity nor specificity uses both true positives and true negatives in the denominator.
NNT in prevention vs treatment US Medical PG Question 4: A 57-year-old man presents to his oncologist to discuss management of small cell lung cancer. The patient is a lifelong smoker and was diagnosed with cancer 1 week ago. The patient states that the cancer was his fault for smoking and that there is "no hope now." He seems disinterested in discussing the treatment options and making a plan for treatment and followup. The patient says "he does not want any treatment" for his condition. Which of the following is the most appropriate response from the physician?
- A. "You seem upset at the news of this diagnosis. I want you to go home and discuss this with your loved ones and come back when you feel ready to make a plan together for your care."
- B. "It must be tough having received this diagnosis; however, new cancer therapies show increased efficacy and excellent outcomes."
- C. "It must be very challenging having received this diagnosis. I want to work with you to create a plan." (Correct Answer)
- D. "We are going to need to treat your lung cancer. I am here to help you throughout the process."
- E. "I respect your decision and we will not administer any treatment. Let me know if I can help in any way."
NNT in prevention vs treatment Explanation: ***"It must be very challenging having received this diagnosis. I want to work with you to create a plan."***
- This response **acknowledges the patient's emotional distress** and feelings of guilt and hopelessness, which is crucial for building rapport and trust.
- It also gently **re-engages the patient** by offering a collaborative approach to treatment, demonstrating the physician's commitment to supporting him through the process.
*"You seem upset at the news of this diagnosis. I want you to go home and discuss this with your loved ones and come back when you feel ready to make a plan together for your care."*
- While acknowledging distress, sending the patient home without further engagement **delays urgent care** for small cell lung cancer, which is aggressive.
- This response might be perceived as dismissive of his immediate feelings and can **exacerbate his sense of hopelessness** and isolation.
*"It must be tough having received this diagnosis; however, new cancer therapies show increased efficacy and excellent outcomes."*
- This statement moves too quickly to treatment efficacy without adequately addressing the patient's current **emotional state and fatalism**.
- While factual, it **lacks empathy** for his personal feelings of blame and hopelessness, potentially making him feel unheard.
*"We are going to need to treat your lung cancer. I am here to help you throughout the process."*
- This response is **too directive and authoritarian**, which can alienate a patient who is already feeling guilty and resistant to treatment.
- It fails to acknowledge his stated feelings of "no hope now" or his disinterest in treatment, which are critical to address before discussing the necessity of treatment.
*"I respect your decision and we will not administer any treatment. Let me know if I can help in any way."*
- While respecting patient autonomy is vital, immediately accepting a patient's decision to refuse treatment without exploring the underlying reasons (e.g., guilt, hopelessness, lack of information) is **premature and potentially harmful**.
- The physician has a responsibility to ensure the patient is making an informed decision, especially for a rapidly progressing condition like small cell lung cancer.
NNT in prevention vs treatment US Medical PG Question 5: An epidemiologist is evaluating the efficacy of Noxbinle in preventing HCC deaths at the population level. A clinical trial shows that over 5 years, the mortality rate from HCC was 25% in the control group and 15% in patients treated with Noxbinle 100 mg daily. Based on this data, how many patients need to be treated with Noxbinle 100 mg to prevent, on average, one death from HCC?
- A. 20
- B. 73
- C. 10 (Correct Answer)
- D. 50
- E. 100
NNT in prevention vs treatment Explanation: ***10***
- The **number needed to treat (NNT)** is calculated by first finding the **absolute risk reduction (ARR)**.
- **ARR** = Risk in control group - Risk in treatment group = 25% - 15% = **10%** (or 0.10).
- **NNT = 1 / ARR** = 1 / 0.10 = **10 patients**.
- This means that **10 patients must be treated with Noxbinle to prevent one death from HCC** over 5 years.
*20*
- This would result from an ARR of 5% (1/0.05 = 20), which is not supported by the data.
- May arise from miscalculating the risk difference or incorrectly halving the actual ARR.
*73*
- This value does not correspond to any standard calculation of NNT from the given mortality rates.
- May result from confusion with other epidemiological measures or calculation error.
*50*
- This would correspond to an ARR of 2% (1/0.02 = 50), which significantly underestimates the actual risk reduction.
- Could result from incorrectly calculating the difference as a proportion rather than absolute percentage points.
*100*
- This would correspond to an ARR of 1% (1/0.01 = 100), grossly underestimating the treatment benefit.
- May result from confusing ARR with relative risk reduction or other calculation errors.
NNT in prevention vs treatment US Medical PG Question 6: A new treatment for hemorrhagic stroke, which is a life-threatening clinical condition that occurs when a diseased blood vessel in the brain ruptures or leaks, was evaluated as soon as it hit the market by an international group of neurology specialists. In those treated with the new drug, a good outcome was achieved in 30%, while those treated with the current standard of care had a good outcome in just 10% of cases. The clinicians involved in this cohort study concluded that the newer drug is more effective and prompted for urgent changes in the guidelines addressing hemorrhagic stroke incidents. According to the aforementioned percentages, how many patients must be treated with the new drug to see 1 additional good outcome?
- A. 5 (Correct Answer)
- B. 30
- C. 20
- D. 15
- E. 10
NNT in prevention vs treatment Explanation: ***Correct: 5***
- This is calculated using the concept of **Number Needed to Treat (NNT)**, which tells us how many patients need to receive the new treatment to see one additional good outcome compared to standard care.
- The **Absolute Risk Reduction (ARR)** is the difference in good outcome rates: 30% - 10% = 20% (or 0.20 as a proportion).
- **NNT = 1 / ARR = 1 / 0.20 = 5**
- Therefore, treating 5 patients with the new drug will result in 1 additional patient with a good outcome compared to standard care.
*Incorrect: 30*
- This represents the **percentage of patients** who achieved a good outcome with the new drug, not the number needed to treat.
- It does not account for the baseline effectiveness of standard treatment, which is essential for calculating the marginal benefit.
- This is the absolute event rate in the treatment group, not a comparative measure.
*Incorrect: 20*
- This is the **Absolute Risk Reduction (ARR)** expressed as a percentage (30% - 10% = 20%).
- While this is a key component in calculating NNT, it is not the NNT itself.
- The NNT requires taking the reciprocal of the ARR when expressed as a proportion: 1/0.20 = 5.
*Incorrect: 15*
- This number does not correspond to any standard epidemiological or biostatistical measure in this context.
- It is neither the ARR, NNT, relative risk, nor any other interpretable value from the given data.
- This is an arbitrary distractor with no mathematical basis.
*Incorrect: 10*
- This represents the **percentage of patients** who achieved a good outcome with standard care (the control group).
- It is the baseline event rate, not a measure of treatment effect or comparative effectiveness.
- Like option 30, it does not reflect the additional benefit from the new treatment.
NNT in prevention vs treatment US Medical PG Question 7: A survey was conducted in a US midwestern town in an effort to assess maternal mortality over the past year. The data from the survey are given in the table below:
Women of childbearing age 250,000
Maternal deaths 2,500
Number of live births 100, 000
Number of deaths of women of childbearing age 7,500
Maternal death is defined as the death of a woman while pregnant or within 42 days of termination of pregnancy from any cause related to or aggravated by, the pregnancy. Which of the following is the maternal mortality rate in this midwestern town?
- A. 1,000 per 100,000 live births
- B. 33 per 100,000 live births
- C. 3,000 per 100,000 live births
- D. 33,300 per 100,000 live births
- E. 2,500 per 100,000 live births (Correct Answer)
NNT in prevention vs treatment Explanation: ***2,500 per 100,000 live births***
- The maternal mortality rate is calculated as the number of **maternal deaths** per 100,000 **live births**. The given data directly provide these values.
- Calculation: (2,500 maternal deaths / 100,000 live births) × 100,000 = **2,500 per 100,000 live births**.
*1,000 per 100,000 live births*
- This value is incorrect as it does not align with the provided numbers for maternal deaths and live births in the calculation.
- It might result from a miscalculation or using incorrect numerator/denominator values from the dataset.
*33 per 100,000 live births*
- This value is significantly lower than the correct rate and suggests a substantial error in calculation or an incorrect understanding of how the maternal mortality rate is derived.
- It could potentially result from dividing the number of live births by maternal deaths, which is the inverse of the correct formula.
*3,000 per 100,000 live births*
- This option is close to the correct answer but slightly higher, indicating a possible calculation error, for instance, including non-maternal deaths or other causes of deaths in the numerator.
- The definition of maternal death is specific to pregnancy-related or aggravated causes, so extraneous deaths would inflate the rate.
*33,300 per 100,000 live births*
- This figure results from incorrectly calculating the proportion of maternal deaths among all deaths of women of childbearing age: (2,500 / 7,500) × 100,000 = 33,333.
- This is a conceptual error as the maternal mortality rate should use live births as the denominator, not total deaths of women of childbearing age.
NNT in prevention vs treatment US Medical PG Question 8: You are currently employed as a clinical researcher working on clinical trials of a new drug to be used for the treatment of Parkinson's disease. Currently, you have already determined the safe clinical dose of the drug in a healthy patient. You are in the phase of drug development where the drug is studied in patients with the target disease to determine its efficacy. Which of the following phases is this new drug currently in?
- A. Phase 4
- B. Phase 1
- C. Phase 2 (Correct Answer)
- D. Phase 0
- E. Phase 3
NNT in prevention vs treatment Explanation: ***Phase 2***
- **Phase 2 trials** involve studying the drug in patients with the target disease to assess its **efficacy** and further evaluate safety, typically involving a few hundred patients.
- The question describes a stage after safe dosing in healthy patients (Phase 1) and before large-scale efficacy confirmation (Phase 3), focusing on efficacy in the target population.
*Phase 4*
- **Phase 4 trials** occur **after a drug has been approved** and marketed, monitoring long-term effects, optimal use, and rare side effects in a diverse patient population.
- This phase is conducted post-market approval, whereas the question describes a drug still in development prior to approval.
*Phase 1*
- **Phase 1 trials** primarily focus on determining the **safety and dosage** of a new drug in a **small group of healthy volunteers** (or sometimes patients with advanced disease if the drug is highly toxic).
- The question states that the safe clinical dose in a healthy patient has already been determined, indicating that Phase 1 has been completed.
*Phase 0*
- **Phase 0 trials** are exploratory, very early-stage studies designed to confirm that the drug reaches the target and acts as intended, typically involving a very small number of doses and participants.
- These trials are conducted much earlier in the development process, preceding the determination of safe clinical doses and large-scale efficacy studies.
*Phase 3*
- **Phase 3 trials** are large-scale studies involving hundreds to thousands of patients to confirm **efficacy**, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug to be used safely.
- While Phase 3 does assess efficacy, it follows Phase 2 and is typically conducted on a much larger scale before submitting for regulatory approval.
NNT in prevention vs treatment US Medical PG Question 9: A research team is working on a new assay meant to increase the sensitivity of testing in cervical cancer. Current sensitivity is listed at 77%. If this research team's latest work culminates in the following results (listed in the table), has the sensitivity improved, and, if so, then by what percentage?
Research team's latest results:
| | Patients with cervical cancer | Patients without cervical cancer |
|--------------------------|-------------------------------|----------------------------------|
| Test is Positive (+) | 47 | 4 |
| Test is Negative (-) | 9 | 44 |
- A. No, the research team has seen a decrease in sensitivity according to the new results listed.
- B. No, the research team has not seen any improvement in sensitivity according to the new results listed.
- C. Yes, the research team has seen an improvement in sensitivity of almost 7% according to the new results listed. (Correct Answer)
- D. Yes, the research team has seen an improvement in sensitivity of more than 10% according to the new results listed.
- E. Yes, the research team has seen an improvement in sensitivity of less than 2% according to new results listed; this improvement is negligible and should be improved upon for significant contribution to the field.
NNT in prevention vs treatment Explanation: ***Yes, the research team has seen an improvement in sensitivity of almost 7% according to the new results listed.***
- **Sensitivity** is calculated as **True Positives / (True Positives + False Negatives)**. From the table: True Positives = 47, False Negatives = 9.
- New sensitivity = 47 / (47 + 9) = 47 / 56 $\approx$ **83.9%**. Compared to the current sensitivity of 77%, this is an improvement of 83.9% - 77% = **6.9%**, which is almost 7%.
*No, the research team has not seen any improvement in sensitivity according to the new results listed.*
- The new sensitivity calculated is **83.9%**, which is indeed higher than the current sensitivity of **77%**.
- This option incorrectly states there is no improvement, as a clear increase of nearly 7% is observed.
*No, the research team has seen a decrease in sensitivity according to the new results listed.*
- The calculated new sensitivity of **83.9%** is higher than the original 77%, indicating an **increase**, not a decrease.
- This statement is factually incorrect based on the provided data.
*Yes, the research team has seen an improvement in sensitivity of more than 10% according to the new results listed.*
- The improvement is approximately **6.9%** (83.9% - 77%), which is less than 10%.
- This option overstates the degree of improvement observed.
*Yes, the research team has seen an improvement in sensitivity of less than 2% according to new results listed; this improvement is negligible and should be improved upon for significant contribution to the field.*
- The calculated improvement is approximately **6.9%**, not less than 2%.
- While clinical significance can be debated, the mathematical calculation of improvement is not accurately reflected by "less than 2%".
NNT in prevention vs treatment US Medical PG Question 10: A pharmaceutical company reports a new antihypertensive drug reduces cardiovascular events with an NNT of 50 over 5 years based on a trial of 10,000 patients. An independent analysis reveals the benefit was driven entirely by a subgroup with resistant hypertension (20% of participants, NNT=15), while the remaining 80% showed no benefit over standard therapy (NNT approaching infinity). Evaluate the ethical and regulatory implications of reporting the overall NNT.
- A. Conduct a new trial in the general hypertensive population to validate efficacy before broader approval
- B. The subgroup analysis represents data dredging; only the overall NNT should be used for clinical decisions
- C. The overall NNT of 50 is statistically valid and appropriate for regulatory approval and marketing
- D. Report both overall and subgroup NNTs; allow clinicians to determine appropriate use based on patient characteristics
- E. The overall NNT is misleading; approval should be restricted to resistant hypertension population where benefit is demonstrated (Correct Answer)
NNT in prevention vs treatment Explanation: ***The overall NNT is misleading; approval should be restricted to resistant hypertension population where benefit is demonstrated***
- Reporting an **aggregate NNT** when the clinical benefit is confined to a specific **subgroup** obscures the fact that the drug is ineffective for 80% of the study population.
- Regulatory and ethical standards dictate that **indication for use** must be limited to populations where a **favorable benefit-risk ratio** has been proven, preventing unnecessary exposure to side effects in non-responders.
*The overall NNT of 50 is statistically valid and appropriate for regulatory approval and marketing*
- While the math is accurate for the trial population as a whole, it ignores **heterogeneity of treatment effect**, which is critical for making safe **clinical recommendations**.
- Marketing a drug based on an **averaged NNT** when the majority of patients derive zero benefit is considered **clinically misleading** and ethically questionable.
*Report both overall and subgroup NNTs; allow clinicians to determine appropriate use based on patient characteristics*
- This approach puts the burden of identifying the correct population on the clinician rather than setting **clear regulatory boundaries** through specific labelling.
- Merely reporting the **overall NNT** may lead to **off-label use** in populations where the NNT is effectively **infinity**, representing a failure in evidence-based guidance.
*Conduct a new trial in the general hypertensive population to validate efficacy before broader approval*
- The existing data already demonstrates that the **general population** (the 80% non-resistant group) showed no benefit over standard therapy.
- Conducting a new trial for the general population would be **unethical and redundant**, as the lack of efficacy in that specific group has already been established by the **independent analysis**.
*The subgroup analysis represents data dredging; only the overall NNT should be used for clinical decisions*
- **Data dredging** refers to finding random patterns; however, identifying a lack of benefit in 80% of a population is a critical **safety and efficacy finding** that cannot be ignored.
- Dismissing the **subgroup effect** would result in potentially treating millions of patients with an **ineffective medication**, violating the principle of **non-maleficence**.
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