Epidemiology Practice Questions

Q: Admission rate bias is?

Berksonian bias. ***Berksonian bias*** - **Berksonian bias** is a form of selection bias, also known as **admission rate bias**, that occurs when different rates of admission to a hospital or clinical setting distort the association between diseases or between a disease and a risk factor. - This bias arises because the hospitalized population may not be representative of the general population, leading to spurious associations or masking real ones. *Reporting bias* - **Reporting bias** is a type of information bias where the outcome or exposure information is reported inaccurately, often due to social desirability or recall issues. - It does not specifically refer to distortions stemming from hospital admission rates. *Response bias* - **Response bias** occurs when participants in a study alter their answers or behavior from what is true due to factors like leading questions, social desirability, or acquiescence. - This is an issue related to data collection, not an unrepresentative study population due to hospital admission protocols. *None of the options* - Berksonian bias directly corresponds to the definition of admission rate bias, making this option incorrect.

Q: What is the expected percentage reduction in mortality risk from breast cancer with annual mammography screening after the age of 50?

15-20%. ***15-20%*** - Current evidence from **meta-analyses and systematic reviews** shows that annual mammography screening in women aged 50 and older reduces breast cancer mortality by approximately **15-20%**. - This estimate is supported by the **U.S. Preventive Services Task Force (USPSTF)** and **Canadian Task Force on Preventive Health Care** based on modern randomized controlled trials. - The benefit reflects **earlier detection** and treatment of breast cancer in this age group. *20-25%* - This range **slightly overestimates** the mortality reduction demonstrated in contemporary evidence-based reviews. - While some older studies reported benefits in this range, more rigorous modern analyses support a lower estimate. *25-30%* - This represents **older estimates** from earlier meta-analyses that have been revised downward with more recent data. - Contemporary evidence-based guidelines do **not support** this level of mortality reduction for routine mammography screening. - This figure may have included methodological biases present in older trials. *30-35%* - This range **significantly overestimates** the mortality benefit of mammography screening. - No current evidence-based guidelines support this level of mortality reduction for average-risk women aged 50 and above. - Such high estimates are not supported by modern randomized controlled trials.

Q: In a class of 100 students, 40 are susceptible to chickenpox. If 28 students developed chickenpox within the next 2 weeks, what is the secondary attack rate (SAR) of chickenpox?

70%. **70% - Correct Answer** The **secondary attack rate (SAR)** measures the spread of disease among susceptible contacts after exposure to a primary case. It is calculated as: **SAR = (Number of new cases among susceptible contacts / Total number of susceptible contacts) × 100%** In this scenario: - New cases = 28 students - Susceptible contacts = 40 students - SAR = (28/40) × 100% = **70%** This is the correct application of the SAR formula, using only susceptible individuals as the denominator (not the total class of 100). *60% - Incorrect* - This would require 24 out of 40 susceptible students developing chickenpox (24/40 = 0.60) - Does not match the observed 28 cases *80% - Incorrect* - This would require 32 out of 40 susceptible students developing chickenpox (32/40 = 0.80) - Overestimates the number of cases compared to the observed 28 *90% - Incorrect* - This would require 36 out of 40 susceptible students developing chickenpox (36/40 = 0.90) - Significantly overestimates the attack rate and does not reflect the actual 28 cases observed

Q: SARS infection case fatality rate of >50% is observed in patients of which age group?

> 65 years. ***> 65 years*** - Patients over 65 years old with **SARS** have been observed to have a **case fatality rate exceeding 50%**, indicating a significantly higher risk of severe outcomes and death in this age group. - This increased vulnerability is often attributed to **weakened immune responses** and higher prevalence of **comorbidities** in older adults. *< 20 yrs* - The case fatality rate for SARS in individuals under 20 years old is observed to be **very low**, typically less than 1%. - This age group generally experiences milder symptoms and has a **more robust immune response** compared to older populations. *20 - 40 years* - In the 20-40 year age group, the case fatality rate for SARS is typically **low to moderate**, generally ranging from 1-5%. - While they are at higher risk than younger individuals, their outcomes are significantly better than those in older age groups. *40 - 60 years* - Patients between 40 and 60 years old with SARS have a moderate case fatality rate, usually in the range of **6-15%**. - This age group shows an elevated risk compared to younger adults but does not reach the very high fatality rates seen in the elderly.

Q: Which of the following correctly describes the components of the epidemiological triad?

Agent, host, environment. **Agent, host, environment** * The **epidemiological triad** is a classic model that describes the interrelationships contributing to disease development. * It consists of the **agent** (the causative factor), the **host** (the organism contracting the disease), and the **environment** (extrinsic factors influencing exposure and susceptibility). * *Time, place, person (descriptive epidemiology)* * **Time, place, and person** are key components of **descriptive epidemiology**, used to characterize disease patterns. * While important for understanding disease distribution, they do not represent the causative interconnectedness of the epidemiological triad. * *Disease, prevention, treatment (healthcare process)* * **Disease, prevention, and treatment** describe aspects of the healthcare process and public health interventions. * They are not the fundamental components used to explain the *occurrence* of disease as modeled by the epidemiological triad. * *Agent, disease, vector (lacks host and environmental components)* * This option includes the **agent** and a **vector** (which is a type of environmental factor or can be considered part of the agent's transmission). * However, it misses the crucial component of the **host** and fully encompassing the broader **environment**.

Q: Secondary attack rate of mumps?

75%. ***75%*** - The **secondary attack rate** for mumps is approximately **75%**, indicating its high transmissibility among susceptible household contacts. - This high rate underscores the importance of vaccination to prevent spread in close-contact settings. *85%* - While mumps is highly contagious, an 85% secondary attack rate is generally considered too high and not reflective of typical epidemiological data. - This percentage is more commonly associated with diseases like measles, which has an even higher transmissibility. *95%* - A 95% secondary attack rate is characteristic of highly contagious diseases like **measles**, which transmit very efficiently even in short, casual contacts. - Mumps, while highly infectious, does not typically reach this level of secondary attack rate. *< 50%* - A secondary attack rate of less than 50% would suggest lower transmissibility than what is observed for mumps. - Diseases with lower secondary attack rates are generally less prone to rapid outbreaks among close contacts.

Q: What is the primary difference between descriptive and analytic studies in epidemiology?

Descriptive studies do not test hypotheses but generate them.. ***Descriptive studies do not test hypotheses but generate them*** - **Descriptive epidemiology** focuses on identifying patterns, trends, and frequencies of health events, often summarized by person, place, and time. - While they do not formally test hypotheses, they are crucial for **generating new hypotheses** that can then be investigated by analytic studies. - This is the **primary and fundamental difference** between descriptive and analytic approaches in epidemiology. *Analytic studies test hypotheses about relationships between health outcomes and exposures* - This statement accurately describes analytic studies, which formally test hypotheses. - However, it only describes one side (analytic) without contrasting it with the key feature of descriptive studies. - It doesn't capture the **primary difference** by showing both sides of the distinction. *Descriptive studies are always retrospective while analytic studies are prospective* - This is **incorrect** - both descriptive and analytic studies can be either retrospective or prospective. - For example, **cohort studies** (analytic) can be retrospective, and **cross-sectional surveys** (descriptive) can be prospective. - Study design timing is independent of whether a study is descriptive or analytic. *Descriptive studies describe the distribution of health outcomes in a population* - This is a correct characteristic of descriptive studies, as they quantify health events by **person, place, and time**. - While true, it only describes what descriptive studies do, without addressing the fundamental difference of **hypothesis generation vs. hypothesis testing**.

Question 1

Admission rate bias is?

Accepted Answer

Berksonian bias

Answer

Reporting bias

Answer

Response bias

Answer

None of the options

Question 2

The difference in incidence between exposed and non-exposed groups in epidemiological studies is best described as:

Accepted Answer

Difference in incidence between exposed and non-exposed groups

Answer

Measure of association between exposure and outcome

Answer

Total impact of exposure on disease occurrence in a population

Answer

Ratio of incidence in exposed versus non-exposed groups

Question 3

What is the expected percentage reduction in mortality risk from breast cancer with annual mammography screening after the age of 50?

Accepted Answer

15-20%

Answer

30-35%

Answer

25-30%

Answer

20-25%

Question 4

During investigation of an epidemic, the area is declared free of epidemic when?

Accepted Answer

Twice the incubation period of the disease since occurrence of the last case

Answer

Thrice the incubation period of the disease since occurrence of the last case

Answer

The longest incubation period for the disease

Answer

Incubation period for the disease plus two standard deviations

Question 5

In a class of 100 students, 40 are susceptible to chickenpox. If 28 students developed chickenpox within the next 2 weeks, what is the secondary attack rate (SAR) of chickenpox?

Accepted Answer

70%

Answer

60%

Answer

90%

Answer

80%

Question 6

SARS infection case fatality rate of >50% is observed in patients of which age group?

Accepted Answer

> 65 years

Answer

< 20 yrs

Answer

20 - 40 years

Answer

40 - 60 years

Question 7

Which of the following correctly describes the components of the epidemiological triad?

Accepted Answer

Agent, host, environment

Answer

Agent, disease, vector

Answer

Time, place, person

Answer

Disease, prevention, treatment

Question 8

Which of the following statements is true regarding the iceberg of disease?

Accepted Answer

The tip of the iceberg represents the clinical cases.

Answer

Screening is primarily done for the tip of the iceberg.

Answer

Hypertension is a classical example of the iceberg of disease.

Answer

The clinician is primarily concerned with the hidden portion of the iceberg.

Question 9

Secondary attack rate of mumps?

Accepted Answer

75%

Answer

95%

Answer

< 50%

Answer

85%

Question 10

What is the primary difference between descriptive and analytic studies in epidemiology?

Accepted Answer

Descriptive studies do not test hypotheses but generate them.

Answer

Analytic studies test hypotheses about relationships between health outcomes and exposures.

Answer

Descriptive studies are always retrospective while analytic studies are prospective.

Answer

Descriptive studies describe the distribution of health outcomes in a population.

Epidemiology — MCQs

Epidemiology — MCQs

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