Sampling methods US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Sampling methods. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Sampling methods US Medical PG Question 1: 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
Sampling methods 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.
Sampling methods US Medical PG Question 2: A clinical trial investigating a new biomedical device used to correct congenital talipes equinovarus (club foot) in infants has recently been published. The study was a preliminary investigation of a new device and as such the sample size is only 20 participants. The results indicate that the new biomedical device is less efficacious than the current standard of care of serial casting (p < 0.001), but the authors mention in the conclusion that it may be due to a single outlier--a patient whose foot remained uncorrected by the conclusion of the study. Which of the following descriptive statistics is the least sensitive to outliers?
- A. Standard deviation
- B. Median (Correct Answer)
- C. Mean
- D. Variance
- E. Mode
Sampling methods Explanation: ***Median***
- The **median** is the middle value in a dataset when ordered from least to greatest, making it inherently resistant to extreme values or **outliers**.
- It describes the central tendency without being skewed by a single unusually high or low data point, unlike the mean.
- Among measures of central tendency, the median is the **most robust** to outliers.
*Standard deviation*
- **Standard deviation** measures the spread of data points around the mean, and because it is based on the **mean**, it is highly sensitive to outliers.
- A single outlier can significantly increase the standard deviation, making the data appear more dispersed than it actually is for the majority of observations.
*Mean*
- The **mean** is calculated by summing all values and dividing by the number of values, which makes it directly affected by every data point, especially extreme ones.
- A single **outlier** can pull the mean significantly towards its value, misrepresenting the central tendency of the majority of the data.
*Variance*
- **Variance** is the average of the squared differences from the mean, and like standard deviation, its calculation heavily relies on the **mean**.
- Squaring the differences amplifies the impact of outliers, making variance very sensitive to extreme values.
*Mode*
- The **mode** represents the most frequently occurring value in a dataset and is also resistant to outliers since it only depends on frequency of occurrence.
- However, in small datasets or datasets without repeated values, the mode may be **undefined or uninformative**, making it less useful for describing central tendency compared to the median.
Sampling methods US Medical PG Question 3: The success of a new treatment designed to deter people from smoking was evaluated by a team of researchers. However, the heaviest and most committed smokers in the study group were less interested in quitting and subsequently dropped out of the study. Nonetheless, the researchers continued with their research (disregarding those who dropped out), which resulted in a false conclusion that the treatment was more successful than the results would have shown under ideal study conditions. The smokers who were confirmed as quitters were actually the ones who were more interested in giving up smoking, which is why they remained in the study. Which of the following is the bias that invalidates the researchers’ conclusion in this example?
- A. Attrition bias (Correct Answer)
- B. Detection bias
- C. Ascertainment bias
- D. Exclusion bias
- E. Non-response bias
Sampling methods Explanation: ***Attrition bias***
- **Attrition bias** occurs when participants drop out of a study in a non-random way, leading to differential loss between study groups. In this case, the more committed smokers, less likely to quit, disproportionately dropped out, making the treatment appear more successful than it was.
- This selective dropout distorts the **study results** because the remaining participants are not representative of the original study population, and the positive outcomes observed are largely due to the loss of those less likely to succeed.
*Detection bias*
- **Detection bias** arises when the outcome of interest is detected unequally between study groups, typically due to different monitoring or diagnostic procedures.
- This bias would involve differences in how smoking cessation was measured or observed, rather than who remained in the study.
*Ascertainment bias*
- **Ascertainment bias** (also known as observer bias or recall bias) occurs when information is collected or interpreted differently due to the observer's expectations or the participant's recall.
- This bias is not concerned with participants dropping out but rather with systematic errors in how data about the outcome is gathered or recalled.
*Exclusion bias*
- **Exclusion bias** can occur when researchers exclude specific individuals or groups from analysis after randomization, often for reasons related to their outcomes or adherence, thereby distorting the results.
- While related to exclusion, **attrition bias** specifically refers to participants *dropping out themselves* in a way that confounds results, rather than being excluded by researchers post-randomization.
*Non-response bias*
- **Non-response bias** typically occurs in surveys or questionnaires when certain types of individuals are less likely to respond, making the sample unrepresentative of the population.
- This bias applies more to initial participation rates in a survey rather than participants dropping out of an intervention study after enrollment.
Sampling methods US Medical PG Question 4: 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?
- A. Phase 0
- B. Phase III
- C. Phase V
- D. Phase II
- E. Phase I (Correct Answer)
Sampling methods Explanation: ***Phase I***
- **Phase I clinical trials** involve a small group of healthy volunteers (typically 20-100) to primarily assess **drug safety**, determine a safe dosage range, and identify side effects.
- The main goal is to establish the **maximum tolerated dose (MTD)** and evaluate the drug's pharmacokinetic and pharmacodynamic profiles.
*Phase 0*
- **Phase 0 trials** are exploratory studies conducted in a very small number of subjects (10-15) to gather preliminary data on a drug's **pharmacodynamics and pharmacokinetics** in humans.
- They involve microdoses, not intended to have therapeutic effects, and thus cannot determine toxicity or MTD.
*Phase III*
- **Phase III trials** are large-scale studies involving hundreds to thousands of patients to confirm the drug's **efficacy**, monitor side effects, compare it to standard treatments, and collect information that will allow the drug to be used safely.
- These trials are conducted after safety and initial efficacy have been established in earlier phases.
*Phase V*
- "Phase V" is not a standard, recognized phase in the traditional clinical trial classification (Phase 0, I, II, III, IV).
- This term might be used in some non-standard research contexts or for post-marketing studies that go beyond Phase IV surveillance, but it is not a formal phase for initial drug development.
*Phase II*
- **Phase II trials** involve several hundred patients with the condition the drug is intended to treat, focusing on **drug efficacy** and further evaluating safety.
- While safety is still monitored, the primary objective shifts to determining if the drug works for its intended purpose and at what dose.
Sampling methods US Medical PG Question 5: Study X examined the relationship between coffee consumption and lung cancer. The authors of Study X retrospectively reviewed patients' reported coffee consumption and found that drinking greater than 6 cups of coffee per day was associated with an increased risk of developing lung cancer. However, Study X was criticized by the authors of Study Y. Study Y showed that increased coffee consumption was associated with smoking. What type of bias affected Study X, and what study design is geared to reduce the chance of that bias?
- A. Observer bias; double blind analysis
- B. Selection bias; randomization
- C. Lead time bias; placebo
- D. Measurement bias; blinding
- E. Confounding; randomization (Correct Answer)
Sampling methods Explanation: ***Confounding; randomization***
- Study Y suggests that **smoking** is a **confounding variable** because it is associated with both increased coffee consumption (exposure) and increased risk of lung cancer (outcome), distorting the apparent relationship between coffee and lung cancer.
- **Randomization** in experimental studies (such as randomized controlled trials) helps reduce confounding by ensuring that known and unknown confounding factors are evenly distributed among study groups.
- In observational studies where randomization is not possible, confounding can be addressed through **stratification**, **matching**, or **multivariable adjustment** during analysis.
*Observer bias; double blind analysis*
- **Observer bias** occurs when researchers' beliefs or expectations influence the study outcome, which is not the primary issue described here regarding the relationship between coffee, smoking, and lung cancer.
- **Double-blind analysis** is a method to mitigate observer bias by ensuring neither participants nor researchers know who is in the control or experimental groups.
*Selection bias; randomization*
- **Selection bias** happens when the study population is not representative of the target population, leading to inaccurate results, which is not directly indicated by the interaction between coffee and smoking.
- While **randomization** is used to reduce selection bias by creating comparable groups, the core problem identified in Study X is confounding, not flawed participant selection.
*Lead time bias; placebo*
- **Lead time bias** occurs in screening programs when early detection without improved outcomes makes survival appear longer, an issue unrelated to the described association between coffee, smoking, and lung cancer.
- A **placebo** is an inactive treatment used in clinical trials to control for psychological effects, and its relevance here is limited to treatment intervention studies.
*Measurement bias; blinding*
- **Measurement bias** arises from systematic errors in data collection, such as inaccurate patient reporting of coffee consumption, but the main criticism from Study Y points to a third variable (smoking) affecting the association, not just flawed measurement.
- **Blinding** helps reduce measurement bias by preventing participants or researchers from knowing group assignments, thus minimizing conscious or unconscious influences on data collection.
Sampling methods US Medical PG Question 6: A resident in the department of obstetrics and gynecology is reading about a randomized clinical trial from the late 1990s that was conducted to compare breast cancer mortality risk, disease localization, and tumor size in women who were randomized to groups receiving either annual mammograms starting at age 40 or annual mammograms starting at age 50. One of the tables in the study compares the two experimental groups with regard to socioeconomic demographics (e.g., age, income), medical conditions at the time of recruitment, and family history of breast cancer. The purpose of this table is most likely to evaluate which of the following?
- A. Observer bias
- B. Statistical power
- C. Confounding
- D. Randomization (Correct Answer)
- E. Effect modification
Sampling methods Explanation: ***Randomization***
- In a randomized clinical trial, the purpose of comparing baseline characteristics between experimental groups is to assess if **randomization successfully distributed potential confounders** evenly.
- An even distribution of baseline characteristics suggests that any observed differences in outcomes are more likely due to the intervention rather than **pre-existing differences** between the groups.
*Observer bias*
- **Observer bias** occurs when researchers' expectations influence their observations or interpretation of results, which is not evaluated by comparing baseline demographics.
- This type of bias is typically mitigated through **blinding** of researchers or participants, rather than checking baseline characteristics.
*Statistical power*
- **Statistical power** refers to the probability of correctly rejecting a false null hypothesis and detecting a true effect.
- It is determined by factors like sample size and effect size, not by the **balance of baseline characteristics** between groups.
*Effect modification*
- **Effect modification** occurs when the effect of an exposure on an outcome varies across different levels of a third variable.
- This is an **analytical consideration** explored in later stages of data analysis, not a concern addressed by comparing baseline characteristics.
*Confounding*
- **Confounding** occurs when an extraneous variable is associated with both the exposure and the outcome, distorting the true relationship.
- While the baseline table helps verify that potential confounders are evenly distributed, the primary purpose is to evaluate whether **randomization was successful**, not to directly assess confounding as an analysis concern.
Sampling methods US Medical PG Question 7: A study is conducted in a hospital to estimate the prevalence of handwashing among healthcare workers. All of the hospital staff members are informed that the study is being conducted for 1 month, and the study method will be a passive observation of their daily routine at the hospital. A total of 89 medical staff members give their consent for the study, and they are followed for a month. This study could most likely suffer from which of the following biases?
- A. Attrition bias
- B. Hawthorne effect (Correct Answer)
- C. Confounding bias
- D. Berksonian bias
- E. Observer-expectancy bias
Sampling methods Explanation: ***Hawthorne effect***
- This bias occurs when individuals modify their behavior in response to being **observed** or knowing they are part of a study. In this scenario, healthcare workers, knowing they are being observed for handwashing, are likely to wash their hands more frequently than usual.
- The intent of the study is to estimate the **prevalence** of handwashing; however, the observed rates will be artificially inflated due to the subjects' awareness of being studied, leading to an inaccurate estimate.
*Attrition bias*
- **Attrition bias** arises when there is **differential loss to follow-up** between study groups, which can lead to biased results.
- This study design involves observing a defined group for a month, but there's no indication of loss of participants or differential dropout from specific intervention or control groups.
*Confounding bias*
- **Confounding bias** occurs when an unmeasured or uncontrolled factor (a **confounder**) is associated with both the exposure and the outcome, distorting the true association.
- While confounding is a common bias in observational studies, the primary issue described here is the direct impact of observation on behavior, not an unmeasured external variable influencing both the behavior and its measurement.
*Berksonian bias*
- **Berksonian bias** (or admission rate bias) is a type of selection bias that occurs in case-control studies when hospital-based controls or cases are used, and the probability of being admitted to the hospital is influenced by both the exposure and the disease itself.
- This study is a **prevalence study** involving direct observation of healthcare workers, not a case-control study, making Berksonian bias irrelevant.
*Observer-expectancy bias*
- **Observer-expectancy bias** occurs when the **researcher's expectations** or beliefs influence their observations or interpretation of data.
- The scenario describes the participants (healthcare workers) changing their behavior due to being observed, not the observer's expectations influencing the recorded data, which would be the **Hawthorne effect**.
Sampling methods US Medical PG Question 8: During identification of severely decomposed remains, which of the following methods provides the most reliable means of positive identification?
- A. Birthmarks
- B. Facial features
- C. DNA analysis (Correct Answer)
- D. Personal effects
Sampling methods Explanation: ***DNA analysis***
- **DNA analysis** remains viable even in significantly degraded samples due to the stability and uniqueness of the genetic code, making it the most reliable method for positive identification of severely decomposed remains.
- It provides a definitive match that is **scientifically verifiable** and rarely subject to error when compared to ante-mortem samples or close relatives.
*Birthmarks*
- **Birthmarks** are soft tissue characteristics that often degrade or become indistinguishable in severely decomposed remains.
- Their presence and appearance can change over time or be obscured by **decomposition processes**, making them unreliable for identification in such cases.
*Facial features*
- **Facial features** rapidly deteriorate and distort after death, especially in severely decomposed remains, making visual recognition impossible.
- The soft tissues of the face are among the first to undergo **autolysis** and putrefaction.
*Personal effects*
- While **personal effects** (like jewelry or clothing) can provide circumstantial evidence, they do not offer positive identification of the individual's remains.
- These items can be easily lost, misplaced, or exchanged, and they do not directly identify the **biological individual**.
Sampling methods US Medical PG Question 9: A research team has data from three completed studies on statin use and Alzheimer's disease: Study A (case-control, OR=0.6, n=500), Study B (retrospective cohort, RR=0.7, n=10,000), and Study C (RCT with cognitive decline as secondary endpoint, RR=0.9, n=2,000). The case-control study used prevalent cases, the cohort study had significant loss to follow-up in the unexposed group, and the RCT was underpowered for cognitive outcomes. Synthesize the evidence to determine the most reliable conclusion about the association.
- A. The RCT provides the strongest evidence despite being underpowered
- B. The retrospective cohort study offers the best balance of validity and precision (Correct Answer)
- C. Case-control study is most reliable due to efficient rare outcome assessment
- D. Evidence is contradictory and no conclusion can be drawn
- E. Meta-analysis of all three studies provides the most accurate estimate
Sampling methods Explanation: ***The retrospective cohort study offers the best balance of validity and precision***
- Despite **differential loss to follow-up** in the unexposed, the very large **sample size (n=10,000)** provides high **statistical power** and precision compared to the other studies.
- Cohort studies establish a **temporal sequence** (statin use before disease onset), which is superior to cross-sectional or prevalent case-control designs for causal inference.
*The RCT provides the strongest evidence despite being underpowered*
- While **Randomized Controlled Trials (RCTs)** are higher in the evidence hierarchy, an **underpowered** study lacks the precision to detect a true effect, increasing the risk of a **Type II error**.
- Since cognitive decline was only a **secondary endpoint**, the study may not have been designed or followed long enough to assess Alzheimer's disease progression accurately.
*Case-control study is most reliable due to efficient rare outcome assessment*
- The use of **prevalent cases** instead of incident cases introduces **Neyman bias (survival bias)**, as it only includes patients who survived long enough to be studied.
- Case-control studies are prone to **recall bias** and cannot definitively prove that statin use preceded the onset of cognitive decline.
*Evidence is contradictory and no conclusion can be drawn*
- While the results vary, researchers can still synthesize evidence by weighing studies based on their **methodological quality**, **sample size**, and **bias profile**.
- A conclusion can be drawn by acknowledging the **conservative estimate** (bias toward the null) in the cohort study which still suggested a protective effect.
*Meta-analysis of all three studies provides the most accurate estimate*
- **Meta-analysis** of studies with fundamentally different designs (RCT, Cohort, Case-Control) and significant **methodological limitations** can lead to inaccurate pooled results ("garbage in, garbage out").
- Combining studies with different measures of association (OR vs RR) and distinct biases like **survival bias** and **differential attrition** increases **heterogeneity**.
Sampling methods US Medical PG Question 10: A public health department needs to determine whether a cluster of birth defects in a county is associated with industrial pollution. They have limited resources, the suspected exposure occurred 3-5 years ago, and the outcome is rare (15 cases identified). Multiple potential confounders exist including maternal age, socioeconomic status, and prenatal care access. The community demands rapid answers. Evaluate the most appropriate initial study design considering feasibility, ethics, and scientific validity.
- A. Prospective cohort study of pregnant women with exposure monitoring
- B. Randomized controlled trial comparing exposed and unexposed areas
- C. Case-control study with multiple control groups and confounder adjustment (Correct Answer)
- D. Ecologic study comparing county-level pollution and birth defect rates
- E. Cross-sectional survey of current pollution levels and birth outcomes
Sampling methods Explanation: ***Case-control study with multiple control groups and confounder adjustment***
- A **case-control study** is the gold standard for investigating **rare outcomes** (only 15 cases identified) because it identifies subjects based on disease status rather than waiting for it to develop.
- This design is highly efficient for **retrospective exposures** that occurred years ago, allows for **rapid results** with limited resources, and can adjust for multiple **confounders** like maternal age and SES through statistical modeling.
*Prospective cohort study of pregnant women with exposure monitoring*
- This design is inappropriate for **rare outcomes** because it would require an massive sample size and many years of follow-up before seeing enough cases to be statistically significant.
- It cannot address a **past exposure** (3-5 years ago) as it follows subjects forward in time from the point of current exposure.
*Randomized controlled trial comparing exposed and unexposed areas*
- It is fundamentally **unethical** to intentionally expose human populations to potentially harmful industrial pollutants in an experimental setting.
- RCTs are used for **interventions** (like new drugs) rather than investigating the etiology of environmental health hazards.
*Ecologic study comparing county-level pollution and birth defect rates*
- This design is prone to the **ecologic fallacy**, where associations found at the population level may not hold true for individuals within that population.
- It cannot adjust for **individual-level confounders** such as personal prenatal care access or specific maternal age, making the results scientifically weaker for the community's needs.
*Cross-sectional survey of current pollution levels and birth outcomes*
- This design suffers from **temporal ambiguity**, as it measures exposure and outcome simultaneously, failing to confirm that pollution Exposure preceded the birth defects.
- Current pollution levels may not accurately reflect the **historical exposure** that occurred during the critical window of embryogenesis 3-5 years ago.
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