Ecological studies — MCQs

10 questions

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 research group designed a study to investigate the epidemiology of syphilis in the United States. The investigators examined per capita income and rates of syphilis in New York City, Los Angeles, Chicago, and Houston. Data on city-wide syphilis rates was provided by each city's health agency. The investigators ultimately found that the number of new cases of syphilis was higher in low-income neighborhoods. This study is best described as which of the following?

A scientist is studying the characteristics of a newly discovered infectious disease in order to determine its features. He calculates the number of patients that develop the disease over several months and finds that on average 75 new patients become infected per month. Furthermore, he knows that the disease lasts on average 2 years before patients are either cured or die from the disease. If the population being studied consists of 7500 individuals, which of the following is the prevalence of the disease?

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 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?

The height of American adults is expected to follow a normal distribution, with a typical male adult having an average height of 69 inches with a standard deviation of 0.1 inches. An investigator has been informed about a community in the American Midwest with a history of heavy air and water pollution in which a lower mean height has been reported. The investigator plans to sample 30 male residents to test the claim that heights in this town differ significantly from the national average based on heights assumed be normally distributed. The significance level is set at 10% and the probability of a type 2 error is assumed to be 15%. Based on this information, which of the following is the power of the proposed study?

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

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 statistician wants to study the effects of a medicine in three groups-humans, animals, and plants. He then selects randomly from these three groups. Which type of sampling is being performed?

Q10

A study was undertaken to establish the relationship between the consumption of a vegetarian or non-vegetarian diet and the presence of diseases. Which statistical test should be used?

Ecological studies US Medical PG Practice Questions and MCQs

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

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 2: A research group designed a study to investigate the epidemiology of syphilis in the United States. The investigators examined per capita income and rates of syphilis in New York City, Los Angeles, Chicago, and Houston. Data on city-wide syphilis rates was provided by each city's health agency. The investigators ultimately found that the number of new cases of syphilis was higher in low-income neighborhoods. This study is best described as which of the following?

A. Double-blind clinical trial
B. Prospective cohort study
C. Case-control study
D. Case series
E. Ecological study (Correct Answer)

Explanation: ***Ecological study*** - This study design examines the relationship between **exposure** (per capita income) and **outcome** (syphilis rates) at the **population level** (cities, neighborhoods) rather than at the individual level. - It uses **aggregate data** from health agencies to identify patterns and correlations, which is characteristic of an ecological study. *Double-blind clinical trial* - A double-blind clinical trial is a type of **interventional study** where neither the participants nor the researchers know who is receiving the treatment versus placebo. - This study is **observational** and does not involve any intervention or blinding. *Prospective cohort study* - A prospective cohort study follows **individuals over time** to see who develops a disease based on their exposure status. - This study does not follow individuals; instead, it looks at **population-level data** at a single point or period. *Case-control study* - A case-control study compares individuals with a disease (**cases**) to individuals without the disease (**controls**) and retrospectively looks for differences in their past exposures. - This study does not identify individual cases and controls or look back at individual exposures. *Case series* - A case series describes the characteristics of a group of patients with a particular disease or exposure. - This study analyzes **population-level income and disease rates**, not detailed clinical information on individual cases.

Question 3: A scientist is studying the characteristics of a newly discovered infectious disease in order to determine its features. He calculates the number of patients that develop the disease over several months and finds that on average 75 new patients become infected per month. Furthermore, he knows that the disease lasts on average 2 years before patients are either cured or die from the disease. If the population being studied consists of 7500 individuals, which of the following is the prevalence of the disease?

A. 0.24 (Correct Answer)
B. 0.02
C. 0.12
D. 0.005
E. 0.01

Explanation: ***0.24*** - Prevalence is calculated as the **number of existing cases** divided by the **total population**. The number of existing cases is estimated by multiplying the **incidence rate** (75 new cases/month) by the **duration of the disease** (2 years or 24 months): 75 cases/month * 24 months = 1800 cases. - The prevalence is then 1800 cases / 7500 individuals = **0.24**. *0.02* - This value might be obtained by incorrectly using only the monthly incidence or by performing **incorrect calculations** involving the duration and total population. - It does not account for the **cumulative effect** of new cases over the entire disease duration. *0.12* - This answer might result from miscalculating the **duration of the disease** (e.g., using 1 year instead of 2 years), leading to an underestimation of the total existing cases. - It suggests an error in converting the **duration from years to months** when multiplying by the monthly incidence. *0.005* - This value is significantly lower than the correct prevalence, suggesting a major error in calculating the total number of cases or incorrectly dividing the total cases by the entire population. - It does not properly reflect the contribution of new cases over the **duration of the disease**. *0.01* - This result is likely derived from an incorrect application of the incidence rate or a misunderstanding of how the duration of the disease impacts the **total number of prevalent cases**. - It's a calculation error that significantly underestimates the **true disease burden**.

Question 4: 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)

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.

Question 5: 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)

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.

Question 6: The height of American adults is expected to follow a normal distribution, with a typical male adult having an average height of 69 inches with a standard deviation of 0.1 inches. An investigator has been informed about a community in the American Midwest with a history of heavy air and water pollution in which a lower mean height has been reported. The investigator plans to sample 30 male residents to test the claim that heights in this town differ significantly from the national average based on heights assumed be normally distributed. The significance level is set at 10% and the probability of a type 2 error is assumed to be 15%. Based on this information, which of the following is the power of the proposed study?

A. 0.10
B. 0.85 (Correct Answer)
C. 0.90
D. 0.15
E. 0.05

Explanation: ***0.85*** - **Power** is defined as **1 - β**, where β is the **probability of a Type II error**. - Given that the probability of a **Type II error (β)** is 15% or 0.15, the power of the study is 1 - 0.15 = **0.85**. *0.10* - This value represents the **significance level (α)**, which is the probability of committing a **Type I error** (rejecting a true null hypothesis). - The significance level is distinct from the **power of the study**, which relates to Type II errors. *0.90* - This value would be the power if the **Type II error rate (β)** was 0.10 (1 - 0.10 = 0.90), but the question specifies a β of 0.15. - It is also the complement of the significance level (1 - α), which is not the definition of power. *0.15* - This value is the **probability of a Type II error (β)**, not the power of the study. - **Power** is the probability of correctly rejecting a false null hypothesis, which is 1 - β. *0.05* - While 0.05 is a common significance level (α), it is not given as the significance level in this question (which is 0.10). - This value also does not represent the power of the study, which would be calculated using the **Type II error rate**.

Question 7: A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

A. "Does the diarrhea typically precede the constipation, or vice-versa?"
B. "Is the diarrhea foul-smelling?"
C. "Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"
D. "Are the symptoms worse in the morning or at night?"
E. "Can you tell me more about the symptoms you have been experiencing?" (Correct Answer)

Explanation: ***Can you tell me more about the symptoms you have been experiencing?*** - This **open-ended question** encourages the patient to provide a **comprehensive narrative** of their symptoms, including details about onset, frequency, duration, alleviating/aggravating factors, and associated symptoms, which is crucial for diagnosis. - In a patient presenting with vague, intermittent symptoms like alternating constipation and diarrhea, allowing them to elaborate freely can reveal important clues that might not be captured by more targeted questions. *Does the diarrhea typically precede the constipation, or vice-versa?* - While knowing the sequence of symptoms can be helpful in understanding the **pattern of bowel dysfunction**, it is a very specific question that might overlook other important aspects of the patient's experience. - It prematurely narrows the focus without first obtaining a broad understanding of the patient's overall symptomatic picture. *Is the diarrhea foul-smelling?* - Foul-smelling diarrhea can indicate **malabsorption** or **bacterial overgrowth**, which are important to consider in some gastrointestinal conditions. - However, this is a **specific symptom inquiry** that should follow a more general exploration of the patient's symptoms, as it may not be relevant if other crucial details are missed. *Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life* - Quantifying pain intensity is useful for assessing the **severity of discomfort** and monitoring changes over time. - However, for a patient with intermittent rather than acute, severe pain, understanding the **character, location, and triggers** of the pain is often more diagnostically valuable than just a numerical rating initially. *Are the symptoms worse in the morning or at night?* - Diurnal variation can be relevant in certain conditions, such as inflammatory bowel diseases where nocturnal symptoms might be more concerning, or functional disorders whose symptoms might be stress-related. - This is another **specific question** that should come after gathering a more complete initial picture of the patient's symptoms to ensure no key information is overlooked.

Question 8: 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

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.

Question 9: A statistician wants to study the effects of a medicine in three groups-humans, animals, and plants. He then selects randomly from these three groups. Which type of sampling is being performed?

A. Simple random sampling
B. Systematic sampling
C. Stratified random sampling (Correct Answer)
D. Cluster sampling
E. Convenience sampling

Explanation: ***Stratified random sampling*** - This method involves dividing the population into **distinct subgroups (strata)** based on shared characteristics (in this case, humans, animals, and plants), and then performing a simple random sample within each stratum. - This ensures that all subgroups are proportionally represented in the sample, which is appropriate when studying effects across different biological categories. *Simple random sampling* - This method involves selecting individuals from the entire population **purely by chance**, without first dividing them into subgroups. - It would not guarantee representation from all three distinct groups (humans, animals, and plants), which is essential for studying differential effects. *Systematic sampling* - This involves selecting samples at **regular intervals** from an ordered list or sequence. - This method is not suitable here because the population is divided into distinct, non-ordered groups rather than a continuous sequence. *Cluster sampling* - This method involves dividing the population into **clusters**, then randomly selecting some clusters and sampling all individuals within those selected clusters. - In this scenario, the initial groups (humans, animals, plants) are strata, not clusters, as the intent is to sample from within each group, not to treat the groups themselves as primary sampling units. *Convenience sampling* - This is a **non-probability sampling method** where subjects are selected based on ease of access rather than random selection. - The question explicitly states that random selection is performed from each group, ruling out convenience sampling.

Question 10: A study was undertaken to establish the relationship between the consumption of a vegetarian or non-vegetarian diet and the presence of diseases. Which statistical test should be used?

A. Chi-square test (Correct Answer)
B. T-test
C. ANOVA
D. Fisher's exact test
E. Mann-Whitney U test

Explanation: ***Chi-square test*** - The **chi-square test** is appropriate when analyzing the relationship between two **categorical variables**. In this scenario, "diet type" (vegetarian/non-vegetarian) and "presence of disease" (yes/no) are both categorical variables. - This test determines if there is a statistically significant association between the frequency counts of these two variables in a contingency table. *T-test* - A **t-test** is used to compare the **means** of two groups, typically when the dependent variable is continuous. - This test is unsuitable here because the presence of disease and diet type are categorical, not continuous, variables. *ANOVA* - **ANOVA** (Analysis of Variance) is used to compare the **means** of three or more groups, often with a continuous dependent variable. - Similar to the t-test, ANOVA is not applicable as the study involves categorical variables, not the comparison of means across multiple groups. *Fisher's exact test* - **Fisher's exact test** is similar to the chi-square test but specifically used for **small sample sizes** where the expected frequencies in any cell of the contingency table are less than 5. - While it analyzes categorical data, the chi-square test is the more general and commonly preferred test for larger sample sizes, which is generally assumed unless otherwise specified. *Mann-Whitney U test* - The **Mann-Whitney U test** is a non-parametric test used to compare differences between two independent groups when the dependent variable is **ordinal or continuous** but not normally distributed. - This test is not appropriate for analyzing the association between two categorical variables, as it requires at least one variable to have ranked or continuous data.

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