Epidemiology — MCQs
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An investigator is studying a new biomarker test to detect breast cancer at early stages. A randomized study is conducted to compare the new test to the current standard of care, mammography, among women over 50 years old. They conclude that breast cancer patients whose cancer was identified by the biomarker lived on average 1.5 years longer than those whose cancers were identified by mammography. If additional independent studies show that there truly was no difference in survival between the two groups, which of the following biases is most likely to have occurred?
In which study design is carry-over effect a PRIMARY methodological concern that requires washout periods between treatment phases?
Ongoing systematic collection, analysis, and interpretation of data, followed by the use of this information to take action for the prevention and control of disease, is known as:
Which one of the following is a dual record system consisting of continuous enumeration of births and deaths, along with an independent survey conducted every six months?
Which of the following best describes a cohort study?
What is the first step an epidemiologist takes in an epidemic investigation?
Descriptive epidemiology studies the distribution and determinants of health-related states or events in specified populations. Which of the following best describes the fundamental components of descriptive epidemiology?
Disability-adjusted life years (DALYs) measure the burden of disease by accounting for both:
Which among the following is the major practical problem in a cohort study?
Which of the following statements is NOT true about a point source epidemic?
Epidemiology Indian Medical PG Practice Questions and MCQs
Question 1821: An investigator is studying a new biomarker test to detect breast cancer at early stages. A randomized study is conducted to compare the new test to the current standard of care, mammography, among women over 50 years old. They conclude that breast cancer patients whose cancer was identified by the biomarker lived on average 1.5 years longer than those whose cancers were identified by mammography. If additional independent studies show that there truly was no difference in survival between the two groups, which of the following biases is most likely to have occurred?
- A. Confounding bias
- B. Test insensitivity
- C. Lead time bias (Correct Answer)
- D. Measurement error
Explanation: ***Lead time bias*** - **Lead time bias** occurs when early detection of a disease, such as through a new biomarker, makes it *appear* that survival has increased, even if the actual disease course or prognosis is unchanged. The patient is simply known to have the disease for a longer period. - In this scenario, the biomarker detects cancer **1.5 years earlier** than mammography. This earlier detection artificially inflates the survival time by 1.5 years (from diagnosis to death), even though both groups die at the same chronological age. The apparent survival benefit is simply due to earlier diagnosis, not improved treatment outcomes. - **Key concept**: If a patient would die at age 70 regardless of when cancer is detected, detecting it at age 65 (biomarker) vs age 68.5 (mammography) creates an apparent 3.5-year vs 2-year survival, despite no actual life extension. *Confounding bias* - **Confounding bias** arises when an unmeasured or uncontrolled factor is associated with both the exposure (biomarker use) and the outcome (survival), distorting the perceived relationship. - While confounding can occur in studies, the described phenomenon (earlier detection appearing to extend survival without changing the disease course) is specifically characteristic of lead time bias, not confounding itself. *Test insensitivity* - **Test insensitivity** refers to a screening test's inability to correctly identify individuals who have a particular disease (i.e., a high false-negative rate or low sensitivity). - This bias would lead to *missing* cases, not to an apparent increase in survival for the cases that *are* detected. *Measurement error* - **Measurement error** involves inaccuracies in the data collection process, such as incorrect recording of survival times or faulty test results. - While measurement errors can affect study outcomes, the systematic difference in apparent survival due to earlier diagnosis without actual prognostic improvement is specifically attributed to lead time bias, not general measurement inaccuracies.
Question 1822: In which study design is carry-over effect a PRIMARY methodological concern that requires washout periods between treatment phases?
- A. Concurrent parallel design
- B. Case-control study
- C. Cohort study
- D. Cross-over study (Correct Answer)
Explanation: ***Correct Option: Cross-over study*** - In a **cross-over study**, each participant receives multiple treatments sequentially, meaning the effects of a previous treatment could carry over to the next treatment phase. - A **washout period** is essential in this design to allow the effects of the prior treatment to dissipate, preventing them from influencing the results of the subsequent treatment. - This is the PRIMARY design where carry-over effects are an inherent methodological concern. *Incorrect Option: Case-control study* - This design compares subjects with a condition (cases) to subjects without the condition (controls) to identify past exposures or risk factors; it does not involve sequential treatments that would lead to a carry-over effect. - The primary concern in case-control studies is **recall bias**, as participants must remember past exposures, not carry-over effects. *Incorrect Option: Concurrent parallel design* - Participants are randomly assigned to one of several treatment groups and receive *only one* treatment throughout the study, eliminating the possibility of a treatment from one phase affecting another. - While it avoids carry-over effects, it often requires a larger sample size compared to cross-over studies to achieve similar statistical power. *Incorrect Option: Cohort study* - This design tracks a defined group of individuals (cohort) over time to observe the incidence of disease and identify risk factors; it does not involve the administration of sequential treatments. - Key concerns in cohort studies include **loss to follow-up** and the potential for a long study duration, rather than carry-over effects.
Question 1823: Ongoing systematic collection, analysis, and interpretation of data, followed by the use of this information to take action for the prevention and control of disease, is known as:
- A. Surveillance (Correct Answer)
- B. Program
- C. Health Planning
- D. Management
Explanation: ***Surveillance*** - This definition perfectly encapsulates the core elements of **public health surveillance**: systematic data collection, analysis, interpretation, and subsequent action for disease prevention and control. - Surveillance is a **continuous process** essential for monitoring health trends, detecting outbreaks, and evaluating interventions. *Program* - A **program** is a set of activities designed to achieve specific goals, but it does not inherently include the continuous, systematic data collection, analysis, and interpretation component. - While public health surveillance can be part of a program, the term "program" itself is broader and lacks the specific epidemiological elements. *Health Planning* - **Health planning** involves setting health objectives, identifying resources, and developing strategies to improve health; however, it is a phase within public health rather than the ongoing process of data use described. - It uses surveillance data but is distinct from the continuous cycle of data collection and action for prevention and control. *Management* - **Management** refers to the coordination and administration of tasks to achieve a goal, which is too general to specifically define the described public health activity. - It lacks the specific focus on **data collection, analysis, interpretation, and action against disease** that is central to surveillance.
Question 1824: Which one of the following is a dual record system consisting of continuous enumeration of births and deaths, along with an independent survey conducted every six months?
- A. Census
- B. Civil registration system
- C. Sample registration system (Correct Answer)
- D. Model registration system
Explanation: ***Sample registration system*** - This system employs a **dual record approach** where a continuous enumeration of births and deaths is conducted by a local enumerator, supplemented by an independent survey every six months. - The collected data from both sources are then **matched and verified** to provide more accurate estimates of vital events, accounting for potential underreporting. *Census* - A **census** is a complete count of the population conducted at regular intervals (e.g., every 10 years) to gather demographic and socioeconomic information. - It provides a **snapshot** of the population at a specific point in time and does not involve continuous enumeration or dual recording of vital events. *Civil registration system* - A **civil registration system** is a legal and administrative process for officially recording vital events such as births, deaths, marriages, and divorces. - While it aims for continuous recording, it typically relies on individuals to report events and does not inherently include a **dual record system** with periodic surveys for verification. *Model registration system* - The term **"model registration system"** is not a widely recognized or standard term for a specific vital event collection methodology. - It might refer to an ideal or exemplary registration system, but it does not describe the specific dual record and survey-based methodology mentioned in the question.
Question 1825: Which of the following best describes a cohort study?
- A. A cross-sectional study that collects data at a single point in time.
- B. A case-control study that compares individuals with a condition to those without.
- C. A study that observes a group of individuals over time to assess the impact of a risk factor. (Correct Answer)
- D. A study that randomly assigns participants to intervention and control groups.
Explanation: ***A study that observes a group of individuals over time to assess the impact of a risk factor.*** - A **cohort study** involves following a group of individuals (the cohort) over a period of time to see how exposure to a **risk factor** affects their outcomes. - It is used to establish the **incidence** of a disease and investigate potential causal relationships. - Cohort studies can be **prospective** (following forward in time) or **retrospective** (using historical data). *A cross-sectional study that collects data at a single point in time.* - A **cross-sectional study** captures data on diseases and risk factors simultaneously at a **single point in time**. - It cannot establish a temporal relationship between exposure and outcome, unlike a cohort study. *A case-control study that compares individuals with a condition to those without.* - A **case-control study** starts with individuals who have a disease (cases) and compares them to individuals who do not have the disease (controls) to look for past **exposures**. - It is **retrospective** and works backward from outcome to exposure, rather than forward from exposure to outcome. *A study that randomly assigns participants to intervention and control groups.* - This describes a **randomized controlled trial (RCT)**, which involves **random assignment** to intervention groups. - Unlike cohort studies (which are **observational**), RCTs involve **active intervention** by researchers.
Question 1826: What is the first step an epidemiologist takes in an epidemic investigation?
- A. Confirm the diagnosis (Correct Answer)
- B. Identify the prone people
- C. Identify the causative factors
- D. Identify the cases
Explanation: ***Confirm the diagnosis*** - The initial and most crucial step is to **confirm the diagnosis** of the disease in question to ensure that the reported cases are indeed suffering from the same condition. - This step helps to avoid misclassification and ensures the investigation focuses on a specific, confirmed health problem. *Identify the cases* - While essential, **identifying cases** usually follows initial diagnostic confirmation, as you need a clear case definition based on a confirmed diagnosis to correctly identify who is a case. - This involves defining who is considered a case based on symptoms, laboratory results, and epidemiological links. *Identify the prone people* - **Identifying prone people** refers to determining the population at risk, which is a subsequent step after understanding the confirmed disease and its initial pattern. - This step typically falls under characterizing the distribution of the disease (person, place, time) in the investigation. *Identify the causative factors* - **Identifying causative factors** is a later stage in the investigation, often involving analytical studies to test hypotheses, which can only occur effectively once the diagnosis is confirmed and cases are clearly defined and counted. - This step aims to understand *why* the epidemic is occurring, after establishing *what* is occurring.
Question 1827: Descriptive epidemiology studies the distribution and determinants of health-related states or events in specified populations. Which of the following best describes the fundamental components of descriptive epidemiology?
- A. Place
- B. Person and Time
- C. Person, Place, and Time (Correct Answer)
- D. All of the options
Explanation: ***Person, Place, and Time*** - The core components of **descriptive epidemiology** are **person (who)**, **place (where)**, and **time (when)**, which are essential for understanding disease patterns. - These elements help describe the **distribution of health-related states** or events, forming the basis for further analytical studies. - Together, they constitute the **epidemiological triad** used to characterize disease occurrence. *Place* - While an important component, **place** alone does not encompass all fundamental aspects of descriptive epidemiology. - Understanding where an event occurs must be combined with **who** is affected and **when** it occurs to provide a complete descriptive picture. *Person and Time* - **Person and time** are two crucial components, but they omit the equally important aspect of **place**. - A comprehensive description requires considering **all three dimensions (who, where, when)** for a full understanding of disease distribution. *All of the options* - This option is incorrect because the other individual options (Place alone, or Person and Time) are **incomplete representations** of descriptive epidemiology. - Only the combination of **all three components together** (Person, Place, and Time) represents the fundamental framework of descriptive epidemiology.
Question 1828: Disability-adjusted life years (DALYs) measure the burden of disease by accounting for both:
- A. None of the options
- B. Morbidity and disability
- C. Mortality and disability (Correct Answer)
- D. Morbidity and mortality
Explanation: ***Mortality and disability*** - **DALYs** quantify the overall burden of disease by combining years of life lost due to **premature mortality** and years lived with disability. - This metric provides a comprehensive measure of disease impact, reflecting both the fatal and non-fatal consequences of illness. *Morbidity and disability* - While both **morbidity** (illness) and **disability** contribute to disease burden, DALYs specifically quantify the years lived with disability, not just the general state of morbidity. - **Morbidity** is a broader term encompassing any illness or disease, which doesn't fully capture the "years lost" component of DALYs. *None of the options* - This option is incorrect because **DALYs** are explicitly defined by the combination of mortality and disability. - The definition of **DALYs** is standard in public health and epidemiology. *Morbidity and mortality* - Although both **morbidity** and **mortality** are crucial aspects of population health, DALYs use **disability** (specifically "years lived with disability" or YLDs) in conjunction with **mortality** ("years of life lost" or YLLs). - Simply using "morbidity" is less precise than "disability" when defining the components of DALYs.
Question 1829: Which among the following is the major practical problem in a cohort study?
- A. Differential loss of follow up (Correct Answer)
- B. Long duration of study
- C. Can be used only for rare conditions
- D. No significant problems with cohort studies.
Explanation: ***Differential loss of follow up*** - **Differential loss to follow-up** occurs when participants lost to follow-up differ systematically concerning exposure and outcome, potentially introducing **selection bias**. - This is a significant practical problem as it can distort the observed association between exposure and outcome, leading to biased results. *Long duration of study* - While **cohort studies** can indeed be **longitudinal** and require a long duration, this is more of an inherent characteristic and resource challenge rather than a "problem" that significantly compromises the validity of the study design itself. - The long duration primarily affects costs and feasibility but doesn't inherently invalidate the findings as much as differential loss to follow-up. *Can be used only for rare conditions* - This statement is incorrect; **cohort studies** are actually **inefficient for rare diseases** because a very large sample size would be needed to observe enough cases of the outcome. - **Case-control studies** are generally preferred for investigating **rare conditions** due to their retrospective outcome-to-exposure design. *No significant problems with cohort studies.* - This statement is incorrect; **cohort studies**, like all observational study designs, have inherent **methodological challenges** and potential sources of bias. - Problems include the **cost** and **time commitment**, **loss to follow-up**, and the potential for **confounding**, all of which require careful consideration in study design and analysis.
Question 1830: Which of the following statements is NOT true about a point source epidemic?
- A. Explosive epidemic
- B. Only one peak
- C. No secondary waves
- D. Plateau phase (Correct Answer)
Explanation: ***Plateau phase*** (Correct Answer - This is NOT true) - A **plateau phase** is characterized by a sustained period of high incidence, which is typical of a **propagated epidemic** where transmission continues over time, **not a point source epidemic**. - In a point source epidemic, due to a single, brief exposure, the number of cases rises sharply and then falls quickly, typically **without a prolonged plateau**. - Point source epidemics show a **sharp rise and rapid fall**, reflecting the fact that all exposures occurred at approximately the same time. *Explosive epidemic* (True statement - not the answer) - This statement is **true** for a point source epidemic, as exposure to the common source often leads to a rapid increase in the number of cases over a short period. - The epidemic curve typically rises sharply and falls quickly, reflecting the **simultaneous exposure** of a large number of susceptible individuals. *Only one peak* (True statement - not the answer) - This statement is **true** for a point source epidemic, as all cases generally occur within one **incubation period** following a single common exposure, resulting in a single, distinct peak in the epidemic curve. - The single peak differentiates it from propagated epidemics, which can have multiple peaks reflecting successive generations of infection. *No secondary waves* (True statement - not the answer) - This statement is **true** for a point source epidemic because everyone exposed to the common source at the same time is infected, and there's no ongoing person-to-person transmission to create subsequent waves. - The epidemic curve will show cases occurring within one **incubation period** following the single exposure.
Practice by Chapter
Principles of Epidemiology
Practice Questions
Measures of Disease Frequency
Practice Questions
Epidemiological Study Designs
Practice Questions
Descriptive Epidemiology
Practice Questions
Analytical Epidemiology
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Experimental Epidemiology
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Screening for Disease
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Surveillance Systems
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Investigation of an Epidemic
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Association and Causation
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Modern Epidemiological Methods
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Critical Appraisal of Epidemiological Studies
Practice Questions
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