Epidemiology Practice Questions

Q: Which type of study is particularly vulnerable to selection bias?

Case control study. ***Case control study*** - Due to the **retrospective nature** of case-control studies, **selection bias** can occur when choosing cases and controls based on their exposure status. - Controls might not be truly representative of the population from which the cases arose, leading to **skewed exposure frequencies** and biased association estimates. *Cohort study* - While cohort studies can experience selection bias, it primarily arises from **differential loss to follow-up** rather than the initial selection process directly affecting exposure assessment. - Participants are typically selected before the outcome occurs, reducing bias related to outcome status influencing selection. *Randomized controlled trial* - **Randomization** is specifically designed to minimize selection bias by ensuring that baseline characteristics, including potential confounders, are evenly distributed between intervention and control groups. - Blinding further reduces the risk of bias from participants or researchers influencing outcomes or exposures. *None of the options* - This option is incorrect because **case-control studies** are indeed particularly susceptible to selection bias due to their design.

Q: If blindness is surveyed using schools as compared to population surveys, then estimation of prevalence of blindness will have?

Underestimation. ***Underestimation*** - School surveys only capture the prevalence of blindness among the **school-going population**, excluding pre-school children and adults. - Many causes of blindness (e.g., **cataract, glaucoma, diabetic retinopathy, age-related macular degeneration**) are more common in older adults, who are not included in school-based surveys, leading to an **underestimation of overall prevalence**. - The majority of blindness burden lies in the **adult and elderly population**, which is completely missed in school surveys. *Overestimation* - An overestimation would occur if the survey sample contained a disproportionately high number of blind individuals compared to the general population, which is unlikely in a school setting. - School surveys tend to exclude populations with higher rates of blindness, making overestimation improbable. *Cannot be compared* - Both school surveys and population surveys can be compared as they are both epidemiological survey methods. - While they survey different populations and serve different purposes, their results can be compared to understand **sampling bias** and **representativeness**. *Remains same* - The prevalence would only remain the same if the demographic and disease characteristics of the school-going population perfectly mirrored those of the general population. - For blindness, this is not the case as the **age distribution** of blindness is heavily skewed toward older ages, which are not represented in school surveys.

Q: Which of the following statements about prevalence is false?

It is a rate. ***It is a rate*** - **Prevalence** is a **proportion**, not a rate, and is calculated as the number of existing cases divided by the total population at a specific point in time or period. - A **rate** measures the frequency of an event over a specified period within a defined population, such as **incidence rate**, which considers new cases over time with a time denominator. - This statement is **FALSE**, making it the correct answer to this negation question. *It is influenced by the duration of disease* - This statement is **true** because a longer **disease duration** means individuals remain "cases" for a longer time, increasing the likelihood of being counted in prevalence calculations. - The relationship follows: **Prevalence ≈ Incidence × Average Duration of Disease**. - Diseases with a **short duration** (e.g., rapidly fatal or rapid recovery) will have lower prevalence, even if their incidence is high. *It includes both new and old cases* - This statement is **true** because **prevalence** counts all existing cases at a given point in time, regardless of when the disease onset occurred. - This distinguishes prevalence from **incidence**, which only counts new cases during a specific time period. - Both recently diagnosed and long-standing cases contribute to the prevalence measure. *It is a proportion* - This statement is **true** because **prevalence** is calculated as a fraction (number of existing cases / total population), which is a characteristic of a **proportion**. - Proportions range from 0 to 1 (or 0% to 100%) and represent a part-to-whole relationship. - Unlike rates, proportions do not have time as an inherent component of the denominator.

Q: The name of the sample group of individuals when followed for successive examinations to evaluate the effect of oral preventive programs is:

Cohort group. ***Cohort group*** - A **cohort group** is a defined group of individuals who share a common characteristic (such as participating in an oral preventive program) and are **followed over time** through successive examinations. - In epidemiological terminology, cohort studies involve longitudinal follow-up to observe outcomes and evaluate intervention effects. - This is the standard term used in most public health and community medicine contexts for groups followed prospectively. *Panel group* - A **panel study** is a specific type of longitudinal study involving repeated measurements on the same individuals over time. - While "panel" accurately describes the repeated examination aspect, **cohort** is the more widely used and accepted term in community medicine and dental public health literature for such follow-up studies. - Panel is sometimes used interchangeably with cohort but is less standard in medical education contexts. *High risk group* - A **high-risk group** refers to individuals with elevated probability of developing a disease or condition. - This term describes **risk status**, not the study design or methodology. - A cohort may include high-risk individuals, but "high-risk group" does not describe the follow-up mechanism. *Prospective group* - **Prospective** describes the **direction of observation** (forward in time) rather than naming the group itself. - While the cohort is studied prospectively, "prospective group" is not standard epidemiological terminology for the group being followed.

Q: Which of the following statements about screening for disease is false?

Arbitrary and final. ***Arbitrary and final*** ✓ **FALSE Statement - Correct Answer** - Screening tests are **NOT arbitrary** - they use **established diagnostic criteria**, validated cutoff points, and standardized protocols - Screening is **NOT final** - positive screening results always require **confirmatory diagnostic tests** before treatment decisions - This statement is false because screening follows **evidence-based protocols** and serves as a **preliminary step** in disease detection, not a definitive diagnosis *Time consuming* - TRUE Statement - Mass screening programs are indeed **time-consuming** due to large population coverage, scheduling logistics, and follow-up requirements - The process includes **participant recruitment**, **test administration**, **result notification**, and **tracking** of screen-positive individuals *Rarely a basis for starting treatment without further confirmation* - TRUE Statement - Screening tests are designed to **identify high-risk individuals** who require further evaluation, not to make treatment decisions - **Confirmatory diagnostic tests** with higher specificity are required before initiating treatment - Starting treatment based solely on screening results risks **overdiagnosis** and **unnecessary interventions** in false-positive cases *Done on apparently healthy people* - TRUE Statement - Screening specifically targets **asymptomatic populations** to detect disease in **preclinical stages** - The goal is **early detection** before symptoms appear, when intervention may be most effective - Distinguishes screening from diagnostic testing, which is performed on symptomatic individuals

Q: In the context of measles, which type of epidemic is characterized by all cases clustering within one incubation period?

Point source epidemic. ***Point source epidemic*** - This type of epidemic occurs when all cases are exposed to the same **common source** over a **brief period**, typically within one incubation period. - The rapid clustering of measles cases suggests a single exposure event to the virus, leading to simultaneous onset of symptoms. - The epidemic curve shows a sharp rise and fall within one incubation period. *Continuous source epidemic* - This involves ongoing exposure to the **common source** over an extended period, resulting in a prolonged epidemic curve with cases presenting over multiple incubation periods. - The epidemic curve shows a plateau pattern as exposure continues. *Propagated epidemic* - Also called **person-to-person epidemic**, this occurs when infection spreads through direct transmission from one person to another. - Cases appear over **several incubation periods** as the disease propagates through the population in successive generations. - The epidemic curve shows multiple peaks corresponding to successive waves of transmission. *Endemic* - An endemic disease is constantly present in a population at a **baseline level**, with a predictable number of cases over time, rather than a sudden clustering. - Measles, if endemic, would show a consistent pattern of cases, not a sudden outbreak over one incubation period.

Q: Which is the best index for assessing the burden of disease?

Disability Adjusted Life Years (DALY). ***Disability Adjusted Life Years (DALY)*** - **DALY** is a comprehensive measure that quantifies the total burden of disease by combining years of life lost due to premature mortality (YLL) and years lived with disability (YLD). - It considers both the **quantity** and **quality of life**, making it an excellent index for assessing the overall impact of diseases on a population. *Case fatality rate (CFR)* - **CFR** measures the proportion of people who die from a specified disease among all individuals diagnosed with the disease within a given period. - While it indicates the **severity** of a disease, it does not account for non-fatal disabling outcomes or years of life lost. *Morbidity rate* - The **morbidity rate** refers to the incidence or prevalence of a disease in a population. - It measures the **frequency** of illness but does not quantify the impact of either premature death or disability. *Dependency ratio* - The **dependency ratio** is an indicator of the age structure of a population, comparing the number of dependants (young and old) to the working-age population. - It relates to the **economic burden** on a society due to age demographics, not directly to the health burden of diseases.

Q: HIV sentinel surveillance is used for:

Monitoring trends in HIV infection. ***Monitoring trends in HIV infection*** - **HIV sentinel surveillance** is specifically designed to track **HIV prevalence trends** over time in selected sentinel populations (ANC attendees, STD clinic attendees, high-risk groups). - The primary objective is to monitor **how HIV infection rates change** over time, helping identify emerging epidemics, evaluate intervention programs, and guide public health policy. - As per **NACO and WHO guidelines**, sentinel surveillance provides repeated cross-sectional prevalence measurements at fixed sites to detect temporal trends in HIV infection. *Monitoring disease trends* - This is **too broad and vague** for the specific purpose of HIV sentinel surveillance. - "Disease trends" could refer to AIDS progression, opportunistic infections, or other disease manifestations, which are **not the focus** of sentinel surveillance. - Sentinel surveillance specifically tracks **infection (seroprevalence)**, not general disease patterns. *Prevalence of HIV infection* - While sentinel surveillance **does measure prevalence**, this is a **method rather than the ultimate purpose**. - Prevalence measurements are taken repeatedly at different time points specifically to **monitor trends**, making this incomplete as the primary objective. *Detection of high-risk group* - Identification of high-risk groups is typically done through **epidemiological studies** and behavioral surveys, not sentinel surveillance. - Sentinel surveillance may **include** high-risk populations as sentinel sites, but its purpose is to monitor trends **within** these groups, not to detect them.

Q: Which blinding technique is considered the most effective in clinical trials?

Double blinding. **Double blinding** - Involves both the **participants** and the **researchers/investigators** being unaware of the treatment assignment. - This method effectively minimizes bias from both **subject expectation** (placebo effect) and **observer expectation** (detection bias). *Single blinding* - Only the **participant** is unaware of the treatment they are receiving, while the investigator knows. - While it reduces participant bias, it can still introduce bias from the investigator regarding **outcome assessment** or **patient interaction**. *Triple blinding* - Extends blinding to include the **data analyst** who is also unaware of the treatment assignments during analysis. - While theoretically offering an additional layer of protection against bias, its practical benefits over double blinding are often marginal and it's less commonly implemented due to **complexity**. *No blinding* - Both the **participants** and the **researchers** are aware of the treatment assignments (open-label study). - This approach is highly susceptible to **bias** from both participant and researcher expectations, significantly compromising the study's validity and reliability.

Q: To determine the endemicity of hepatitis B, what should be measured?

HBsAg (Hepatitis B surface antigen). ***HBsAg*** - **HBsAg (Hepatitis B surface antigen)** is the primary marker used to determine the **endemicity** of hepatitis B because its persistent presence indicates **chronic infection**. - A high prevalence of HBsAg in a population signifies a high burden of chronic hepatitis B infection, reflecting the endemic nature of the disease in that region. *HBcAg (Hepatitis B core antigen)* - **HBcAg** is an **intracellular antigen** and is not detectable in the serum, making it unsuitable for population-level screening or endemicity assessment. - While important for viral replication, its absence in routine blood tests means it cannot be used to gauge the prevalence of infection in a community. *HBeAg (Hepatitis B e antigen)* - **HBeAg** indicates **active viral replication** and high infectivity but is not the best marker for overall endemicity. - A positive HBeAg suggests active disease and high transmissibility in an infected individual, but not the general prevalence of chronic infection in a population. *Anti-HBeAg (Hepatitis B e antibody)* - **Anti-HBeAg** indicates a **decrease in viral replication** and a lower risk of transmission, often representing a stage of immune control. - While useful for monitoring disease progression, it is an antibody response and does not directly measure the presence of chronic infection or endemicity.

Question 1

Which type of study is particularly vulnerable to selection bias?

Accepted Answer

Case control study

Answer

Cohort study

Answer

Randomized controlled trial

Answer

None of the options

Question 2

If blindness is surveyed using schools as compared to population surveys, then estimation of prevalence of blindness will have?

Accepted Answer

Underestimation

Answer

Cannot be compared

Answer

Overestimation

Answer

Remains same

Question 3

Which of the following statements about prevalence is false?

Accepted Answer

It is a rate

Answer

It is influenced by the duration of disease

Answer

It includes both new and old cases

Answer

It is a proportion

Question 4

The name of the sample group of individuals when followed for successive examinations to evaluate the effect of oral preventive programs is:

Accepted Answer

Cohort group

Answer

Panel group

Answer

High risk group

Answer

Prospective group

Question 5

Which of the following statements about screening for disease is false?

Accepted Answer

Arbitrary and final

Answer

Time consuming

Answer

Rarely a basis for starting treatment without further confirmation

Answer

Done on apparently healthy people

Question 6

In the context of measles, which type of epidemic is characterized by all cases clustering within one incubation period?

Accepted Answer

Point source epidemic

Answer

Continuous source epidemic

Answer

Propagated epidemic

Answer

Endemic

Question 7

Which is the best index for assessing the burden of disease?

Accepted Answer

Disability Adjusted Life Years (DALY)

Answer

Case fatality rate (CFR)

Answer

Morbidity rate

Answer

Dependency ratio

Question 8

HIV sentinel surveillance is used for:

Accepted Answer

Monitoring trends in HIV infection

Answer

Detection of high-risk group

Answer

Prevalence of HIV infection

Answer

Monitoring disease trends

Question 9

Which blinding technique is considered the most effective in clinical trials?

Accepted Answer

Double blinding

Answer

Triple blinding

Answer

No blinding

Answer

Single blinding

Question 10

To determine the endemicity of hepatitis B, what should be measured?

Accepted Answer

HBsAg (Hepatitis B surface antigen)

Answer

HBcAg (Hepatitis B core antigen)

Answer

HBeAg (Hepatitis B e antigen)

Answer

Anti-HBeAg (Hepatitis B e antibody)

Epidemiology — MCQs

Epidemiology — MCQs

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