Calculation from absolute risk reduction US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Calculation from absolute risk reduction. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Calculation from absolute risk reduction US Medical PG Question 1: A 35-year-old woman is started on a new experimental intravenous drug X. In order to make sure that she is able to take this drug safely, the physician in charge of her care calculates the appropriate doses to give to this patient. Data on the properties of drug X from a subject with a similar body composition to the patient is provided below:
Weight: 100 kg
Dose provided: 1500 mg
Serum concentration 15 mg/dL
Bioavailability: 1
If the patient has a weight of 60 kg and the target serum concentration is 10 mg/dL, which of the following best represents the loading dose of drug X that should be given to this patient?
- A. 300 mg
- B. 450 mg
- C. 150 mg
- D. 1000 mg
- E. 600 mg (Correct Answer)
Calculation from absolute risk reduction Explanation: ***600 mg***
- First, calculate the **volume of distribution (Vd)** using the provided data: **Vd = Total Dose / Serum Concentration**. Converting units: 15 mg/dL = 150 mg/L. Therefore, Vd = 1500 mg / 150 mg/L = **10 L** (for the 100 kg subject).
- Since the Vd value is for a 100 kg person, Vd per kg = 10 L / 100 kg = **0.1 L/kg**. For the 60 kg patient, the Vd = 0.1 L/kg × 60 kg = **6 L**.
- The **loading dose = Target Serum Concentration × Vd / Bioavailability**. Converting target concentration: 10 mg/dL = 100 mg/L. Therefore: (100 mg/L × 6 L) / 1 = **600 mg**.
*300 mg*
- This value is obtained if an incorrect **Vd** or target concentration was used, potentially through miscalculation or incorrect unit conversion.
- For instance, if the **Vd** was inaccurately calculated at 3 L (instead of 6 L), this could lead to the incorrect answer.
*450 mg*
- This result might occur if the **Vd calculation** was flawed or if the target concentration was incorrectly interpreted.
- A potential error could involve using a Vd of 4.5 L which would result in 450 mg, or if the drug amount was simply prorated by weight without properly considering the Vd per kg.
*150 mg*
- This value suggests a significant error in the calculation of the **volume of distribution** or the target concentration.
- It might be obtained if the **Vd** was mistakenly taken as 1.5 L or if the dose was divided by the original serum concentration without accounting for the new patient's weight and desired concentration.
*1000 mg*
- This value is significantly higher than the correct answer, indicating an overestimation of the **Vd** or target concentration.
- It could result from using the original dose (1500 mg) and attempting to scale it incorrectly by weight alone (1500 mg × 60/100 = 900 mg, close to 1000), or if unit conversions were mishandled during the Vd determination.
Calculation from absolute risk reduction US Medical PG Question 2: A researcher is designing an experiment to examine the toxicity of a new chemotherapeutic agent in mice. She splits the mice into 2 groups, one of which she exposes to daily injections of the drug for 1 week. The other group is not exposed to any intervention. Both groups are otherwise raised in the same conditions with the same diet. One month later, she sacrifices the mice to check for dilated cardiomyopathy. In total, 52 mice were exposed to the drug, and 50 were not exposed. Out of the exposed group, 13 were found to have dilated cardiomyopathy on necropsy. In the unexposed group, 1 mouse was found to have dilated cardiomyopathy. Which of the following is the relative risk of developing cardiomyopathy with this drug?
- A. 12.5 (Correct Answer)
- B. 25.0
- C. 13.7
- D. 16.3
- E. 23.0
Calculation from absolute risk reduction Explanation: ***Correct Option: 12.5***
- The **relative risk (RR)** is calculated as the **risk in the exposed group divided by the risk in the unexposed group**: RR = [a/(a+b)] / [c/(c+d)]
- **Risk in exposed group** = 13/52 = 0.25 (25%)
- **Risk in unexposed group** = 1/50 = 0.02 (2%)
- **RR = 0.25 / 0.02 = 12.5**
- This indicates that mice exposed to the chemotherapeutic agent are **12.5 times more likely** to develop dilated cardiomyopathy compared to unexposed mice
- An **RR > 1** indicates increased risk with exposure, supporting the drug's cardiotoxicity
*Incorrect Option: 25.0*
- This value results from **miscalculating the unexposed group risk** (e.g., using 0.01 instead of 0.02 as the denominator)
- If the unexposed risk was halved incorrectly: 0.25 / 0.01 = 25.0
- This overestimates the relative risk by a factor of 2
*Incorrect Option: 13.7*
- This value does not result from the correct **relative risk formula**
- May arise from an **arithmetic error** or confusion with other epidemiological measures
- The correct calculation of 13/52 ÷ 1/50 does not yield this result
*Incorrect Option: 16.3*
- This might result from **miscounting the number of subjects** in either group or confusing **relative risk with odds ratio**
- The **odds ratio** would be calculated as (13/39) / (1/49) = 16.3
- Remember: **Relative risk uses total exposed/unexposed as denominators**, while odds ratio uses non-diseased counts
*Incorrect Option: 23.0*
- This value suggests a **fundamental error** in applying the relative risk formula
- Could result from using incorrect numerators or denominators (e.g., 13/1 instead of proper risk calculation)
- Significantly overestimates the true relative risk of 12.5
Calculation from absolute risk reduction US Medical PG Question 3: You are reading through a recent article that reports significant decreases in all-cause mortality for patients with malignant melanoma following treatment with a novel biological infusion. Which of the following choices refers to the probability that a study will find a statistically significant difference when one truly does exist?
- A. Type II error
- B. Type I error
- C. Confidence interval
- D. p-value
- E. Power (Correct Answer)
Calculation from absolute risk reduction Explanation: ***Power***
- **Power** is the probability that a study will correctly reject the null hypothesis when it is, in fact, false (i.e., will find a statistically significant difference when one truly exists).
- A study with high power minimizes the risk of a **Type II error** (failing to detect a real effect).
*Type II error*
- A **Type II error** (or **beta error**) occurs when a study fails to reject a false null hypothesis, meaning it concludes there is no significant difference when one actually exists.
- This is the **opposite** of what the question describes, which asks for the probability of *finding* a difference.
*Type I error*
- A **Type I error** (or **alpha error**) occurs when a study incorrectly rejects a true null hypothesis, concluding there is a significant difference when one does not actually exist.
- This relates to the **p-value** and the level of statistical significance (e.g., p < 0.05).
*Confidence interval*
- A **confidence interval** provides a range of values within which the true population parameter is likely to lie with a certain degree of confidence (e.g., 95%).
- It does not directly represent the probability of finding a statistically significant difference when one truly exists.
*p-value*
- The **p-value** is the probability of observing data as extreme as, or more extreme than, that obtained in the study, assuming the null hypothesis is true.
- It is used to determine statistical significance, but it is not the probability of detecting a true effect.
Calculation from absolute risk reduction US Medical PG Question 4: 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
Calculation from absolute risk reduction 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.
Calculation from absolute risk reduction US Medical PG Question 5: In 2006, three researchers from North Carolina wanted to examine the benefits of treating the risk of suicidality in children and adolescents by looking at randomized, multicenter, controlled trials of sertraline usage compared to placebo. Their analysis found clinically significant benefits of the drug and a positive benefit-to-risk ratio for sertraline in adolescents with major depressive disorder. They also found that 64 depressed children and adolescents need to receive the drug for 1 extra patient to experience suicidality as an adverse outcome. In other words, if 64 treated individuals received sertraline, some would experience suicidality due to their illness, some would not experience suicidality, and 1 individual would become suicidal due to the unique contribution of sertraline. Which of the following statements is true for this measure (defined as the inverse of the attributable risk), which aims to describe adverse outcomes this way?
- A. Higher measures indicate greater risk.
- B. Input values must be probabilities of the events of interest. (Correct Answer)
- C. Multiple risks can be contained and described within one result.
- D. The final metric represents proportions in percentage terms.
- E. The measure can include multiple events at one time.
Calculation from absolute risk reduction Explanation: ***Input values must be probabilities of the events of interest.***
- The measure described (- the inverse of the **attributable risk** - or more accurately, the **Number Needed to Harm** or **NNH**) is derived from **absolute risk reduction**, which requires the risk of an event in the exposed group and the risk of the event in the unexposed/control group to be expressed as **probabilities or proportions**.
- These probabilities are essential for calculating the difference in event rates, which is then inverted to get the NNH.
*Higher measures indicate greater risk.*
- A **higher NNH** (e.g., 64 in this case) indicates that a larger number of patients need to be treated for one additional adverse event to occur, implying a **lower risk** associated with the treatment.
- Conversely, a **lower NNH** (e.g., 10) would mean fewer patients need to be treated for one additional adverse event, indicating a **higher risk**.
*Multiple risks can be contained and described within one result.*
- The NNH (or Number Needed to Treat) is typically calculated for a **single specific outcome** (either beneficial or harmful).
- While an overall benefit-to-risk analysis might involve considering multiple outcomes, the NNH itself quantifies the impact for **one defined event**.
*The final metric represents proportions in percentage terms.*
- The final metric (NNH) is expressed as a **whole number** (e.g., 64), representing the number of patients.
- It does **not represent a proportion or a percentage**; rather, it indicates how many individuals need to be exposed to experience one additional event.
*The measure can include multiple events at one time.*
- The NNH is event-specific; it calculates the number of patients for **one particular adverse event**.
- To analyze multiple events, one would need to calculate **separate NNH values** for each individual event.
Calculation from absolute risk reduction US Medical PG Question 6: 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
Calculation from absolute risk reduction 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.
Calculation from absolute risk reduction US Medical PG Question 7: A researcher is investigating the effects of a new antihypertensive medication on renal physiology. She gives a subject a dose of the new medication, and she then collects plasma and urine samples. She finds the following: Hematocrit: 40%; Serum creatinine: 0.0125 mg/mL; Urine creatinine: 1.25 mg/mL. Urinary output is 1 mL/min. Renal blood flow is 1 L/min. Based on the above information and approximating that the creatinine clearance is equal to the GFR, what answer best approximates filtration fraction in this case?
- A. 10%
- B. 17% (Correct Answer)
- C. 33%
- D. 50%
- E. 25%
Calculation from absolute risk reduction Explanation: ***17%***
- First, calculate **GFR** using the creatinine clearance formula: GFR = (Urine creatinine × Urinary output) / Serum creatinine = (1.25 mg/mL × 1 mL/min) / 0.0125 mg/mL = **100 mL/min**.
- Next, calculate **Renal Plasma Flow (RPF)** from Renal Blood Flow (RBF) and Hematocrit: RPF = RBF × (1 - Hematocrit) = 1000 mL/min × (1 - 0.40) = **600 mL/min**.
- Finally, calculate **Filtration Fraction (FF)** = GFR / RPF = 100 mL/min / 600 mL/min = 0.1667 = **16.7%, which approximates to 17%**.
- This is the correct answer based on the physiological calculations and represents a normal filtration fraction.
*10%*
- This would correspond to a filtration fraction of 0.10, which would require either a GFR of 60 mL/min (lower than calculated) or an RPF of 1000 mL/min (higher than calculated).
- This value is too low given the provided parameters and doesn't match the calculation from the given data.
*25%*
- This value would suggest FF = 0.25, requiring a GFR of 150 mL/min with the calculated RPF of 600 mL/min.
- This is higher than the calculated GFR of 100 mL/min and doesn't match the given creatinine values.
*33%*
- This would imply FF = 0.33, requiring a GFR of approximately 200 mL/min with RPF of 600 mL/min.
- This is significantly higher than the calculated GFR and would represent an abnormally elevated filtration fraction.
*50%*
- A filtration fraction of 50% is unphysiologically high and would indicate severe pathology.
- This would require a GFR of 300 mL/min with the calculated RPF, which is impossible given the provided creatinine clearance data.
Calculation from absolute risk reduction US Medical PG Question 8: You are reviewing raw data from a research study performed at your medical center examining the effectiveness of a novel AIDS screening examination. The study enrolled 250 patients with confirmed AIDS, and 240 of these patients demonstrated a positive screening examination. The control arm of the study enrolled 250 patients who do not have AIDS, and only 5 of these patients tested positive on the novel screening examination. What is the NPV of this novel test?
- A. 240 / (240 + 15)
- B. 240 / (240 + 5)
- C. 240 / (240 + 10)
- D. 245 / (245 + 10) (Correct Answer)
- E. 245 / (245 + 5)
Calculation from absolute risk reduction Explanation: ***245 / (245 + 10)***
- The **negative predictive value (NPV)** is calculated as **true negatives (TN)** divided by the sum of **true negatives (TN)** and **false negatives (FN)**.
- In this study, there are 250 patients with AIDS; 240 tested positive (true positives, TP), meaning 10 tested negative (false negatives, FN = 250 - 240). There are 250 patients without AIDS; 5 tested positive (false positives, FP), meaning 245 tested negative (true negatives, TN = 250 - 5). Therefore, NPV = 245 / (245 + 10).
*240 / (240 + 15)*
- This calculation incorrectly uses the number of **true positives** (240) in the numerator and denominator, which is relevant for **positive predictive value (PPV)**, not NPV.
- The denominator `(240 + 15)` does not correspond to a valid sum for calculating NPV from the given data.
*240 / (240 + 5)*
- This calculation incorrectly uses **true positives** (240) in the numerator, which is not part of the NPV formula.
- The denominator `(240 + 5)` mixes true positives and false positives, which is incorrect for NPV.
*240 / (240 + 10)*
- This incorrectly places **true positives** (240) in the numerator instead of **true negatives**.
- The denominator `(240+10)` represents **true positives + false negatives**, which is related to sensitivity, not NPV.
*245 / (245 + 5)*
- This calculation correctly identifies **true negatives** (245) in the numerator but incorrectly uses **false positives** (5) in the denominator instead of **false negatives**.
- The denominator for NPV should be **true negatives + false negatives**, which is 245 + 10.
Calculation from absolute risk reduction US Medical PG Question 9: A first time mother of a healthy, full term, newborn girl is anxious about sudden infant death syndrome. Which of the following pieces of advice can reduce the risk of SIDS?
- A. Sleep supine in a crib with bumpers, head propped up on a pillow, and wrapped in a warm blanket
- B. Sleep supine in a crib with bumpers, head propped up on a pillow, and wrapped in an infant sleeper
- C. Sleep supine in the parent's bed and use a pacifier after 1 month of age
- D. Sleep supine in a crib without bumpers, use a pacifier after 1 month of age, and use a home apnea monitor
- E. Sleep supine in a crib without bumpers, use a pacifier after 1 month of age, and avoid smoking (Correct Answer)
Calculation from absolute risk reduction Explanation: ***Sleep supine in a crib without bumpers, use a pacifier after 1 month of age, and avoiding smoking***
- **Sleeping supine** (on the back) is the most critical recommendation to reduce SIDS risk, and a **crib without bumpers** and other soft bedding reduces smothering hazards.
- **Pacifier use** after the first month of age has been shown to be protective, and **avoiding smoking** around the infant is crucial as exposure to tobacco smoke significantly increases SIDS risk.
*Sleep supine in a crib with bumpers, head propped up on a pillow, and wrapped in a warm blanket*
- While **sleeping supine** is correct, **bumpers, pillows, and loose blankets** in the crib are significant risk factors for SIDS, as they can cause accidental suffocation.
- The use of **pillows** is not recommended for infants due to the risk of airway obstruction and suffocation.
*Sleep supine in a crib with bumpers, head propped up on a pillow, and wrapped in an infant sleeper*
- Similar to the previous option, **bumpers and a pillow** are unsafe as they pose a suffocation risk and should be avoided in an infant's sleep environment.
- While an **infant sleeper** (or sleep sack) is generally safer than a loose blanket, the presence of bumpers and a pillow negates this benefit.
*Sleep supine in the parent's bed and use a pacifier after 1 month of age*
- **Co-sleeping (sharing a bed with parents)** significantly increases the risk of SIDS and accidental suffocation, especially if parents smoke, are impaired, or if heavy bedding is present.
- Although **pacifier use** is recommended, sleeping in the parent's bed is a major risk factor that outweighs any potential benefit here.
*Sleep supine in a crib without bumpers, use a pacifier after 1 month of age, and use a home apnea monitor*
- While **sleeping supine** in a **crib without bumpers** and **pacifier use** are correct recommendations, **home apnea monitors** are not recommended for routine SIDS prevention in healthy infants.
- Apnea monitors have not been shown to reduce the incidence of SIDS and can lead to false alarms and unnecessary anxiety without proven benefit.
Calculation from absolute risk reduction US Medical PG Question 10: 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?
- A. 0.75
- B. 0.04
- C. 0.5
- D. 0.06 (Correct Answer)
- E. 0.02
Calculation from absolute risk reduction Explanation: ***0.06***
- The **risk of myocardial infarction** in participants with psoriasis is calculated by dividing the number of psoriasis patients who had a myocardial infarction by the total number of psoriasis patients.
- This calculation is 12 (myocardial infarctions in psoriasis group) / 200 (total psoriasis patients) = **0.06 or 6%**.
- This represents the **cumulative incidence** or **absolute risk** in the exposed cohort over 10 years.
*0.75*
- This value represents the **proportion of all MI cases that occurred in the psoriasis group**: 12/16 = 0.75.
- This is not the same as risk, which requires the denominator to be the total at-risk population (all psoriasis patients), not just those with the outcome.
*0.04*
- This value represents the **risk of myocardial infarction in the control group** (no psoriasis): 4/200 = 0.02, not 0.04.
- However, 0.04 could represent 2 × 0.02, which has no meaningful epidemiological interpretation for this study.
*0.5*
- This value does not correspond to any standard epidemiological measure from the given data.
- It might represent a miscalculation or confusion with other statistical concepts.
*0.02*
- This value represents the **risk of myocardial infarction in the unexposed group** (no psoriasis): 4/200 = 0.02 or 2%.
- The question specifically asks for the risk in the psoriasis group, not the control group.
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