Epidemiology Practice Questions

Q: Berksonian bias is a selection bias which occurs in

Hospital based studies. ***Hospital based studies*** - **Berksonian bias** is a type of **selection bias** that occurs when the study population is drawn from a hospital or clinical setting. - This can lead to an artificially inflated or deflated association between risk factors and diseases, as hospital patients often have multiple health conditions or risk factors not representative of the general population. *Natural exposure studies* - These studies observe populations exposed to a factor naturally, without intervention, and are less prone to selection bias related to hospital admission. - While other biases can occur, **Berksonian bias** specifically relates to admission criteria for healthcare facilities. *Community based studies* - **Community-based studies** aim to recruit participants from the general population, making them less susceptible to **Berksonian bias** compared to hospital-based studies. - They strive for a more representative sample, reducing the selection pressures seen in clinical settings. *Laboratory based studies* - **Laboratory studies** typically use controlled environments and experimental designs, often involving cell cultures or animal models. - They are generally not subject to **Berksonian bias**, which is specific to human population studies drawing from clinical settings.

Q: Match the diseases in List-I with their respective incubation periods in List-II and select the correct answer using the code given below:

A→1 B→2 C→3 D→4. ***A→1 B→2 C→3 D→4*** - This option correctly matches **Measles (A)** with **10-14 days (1)**, which is the accurate incubation period for this **paramyxovirus infection**. - It properly pairs **Diphtheria (B)** with **2-6 days (2)**, reflecting the typical incubation period for **Corynebacterium diphtheriae**. - **Hepatitis A (C)** is correctly matched with **15-50 days (3)**, consistent with the incubation period of this **hepatotropic picornavirus**. - **Hepatitis B (D)** is correctly matched with **6 weeks-6 months (4)**, reflecting the prolonged incubation period of this **hepadnavirus**. *A→3 B→4 C→2 D→1* - This option incorrectly assigns **Measles** to **15-50 days**, which is far too long for this **viral exanthem** that typically manifests within **10-14 days**. - It also mismatches **Diphtheria** with **6 weeks-6 months**, when this **bacterial infection** has a much shorter incubation period of **2-6 days**. *A→4 B→3 C→2 D→1* - This option incorrectly assigns **Measles** to **6 weeks-6 months**, which is excessively long for this **acute viral infection**. - It also misplaces **Hepatitis A** to **2-6 days**, when its actual incubation period is much longer at **15-50 days**. *A→1 B→4 C→3 D→2* - This option correctly matches **Measles** with **10-14 days** but incorrectly assigns **Diphtheria** to **6 weeks-6 months** instead of the correct **2-6 days**. - It also mismatches **Hepatitis B** to **2-6 days**, when it actually has a much longer incubation period of **6 weeks-6 months**.

Q: The net reproduction rate of 1 is primarily determined by which of the following demographic rates?

Total fertility rate. ***Total fertility rate*** - The **Net Reproduction Rate (NRR)** is a refinement of the **Gross Reproduction Rate (GRR)**, which itself is derived from the **Total Fertility Rate (TFR)**. - An NRR of 1 implies that a generation of women is exactly replacing itself, meaning that, on average, each woman is giving birth to enough daughters who survive to reproductive age to take her place. This is directly linked to the overall fertility level represented by the Total Fertility Rate. *Couple protection rate* - The **couple protection rate** measures the percentage of eligible couples effectively protected against conception, typically through family planning methods. - While it influences the **Total Fertility Rate**, it is not the primary determinant of the **Net Reproduction Rate** itself. *Total marital fertility rate* - The **total marital fertility rate** measures the average number of children born to a woman within marriage. - It does not account for births outside of marriage or for the mortality of women before or during their reproductive years, which are crucial components of the **Net Reproduction Rate**. *Age specific marital fertility rate* - The **age-specific marital fertility rate** measures the number of births to married women within a specific age group. - This is a more granular component of fertility measurement but not the primary determinant of the overall replacement level indicated by an **NRR of 1**, which requires a broader measure like the **Total Fertility Rate**.

Q: The useful fertility indicator where birth registration statistics do not exist or are inadequate is :

Child-woman ratio. ***Child-woman ratio*** - The **child-woman ratio** is a common **fertility indicator** used in areas where reliable birth registration data is unavailable. - It calculates the number of **children under 5 years old per 1000 women of childbearing age** (typically 15-49 years), providing an estimate of recent fertility. *Abortion rate* - The **abortion rate** measures the number of abortions per 1,000 women of reproductive age. - While it reflects a component of reproductive behavior, it does not directly measure live births or general fertility and relies on accurate abortion statistics which may also be inadequate. *Net reproduction rate* - The **net reproduction rate (NRR)** is a sophisticated measure that indicates the average number of daughters a woman will have if she survives to the end of her reproductive years, taking into account mortality. - This indicator requires **detailed birth and death statistics by age**, which are precisely what are lacking when birth registration is inadequate. *Male-female ratio* - The **male-female ratio**, or sex ratio, compares the number of males to females in a population. - This ratio is a demographic indicator used to understand population structure but **does not directly measure fertility**.

Q: A village has a total of 100 under-five children. The coverage with measles vaccine in these age groups is 60%. Following the occurrence of a measles case in a child after a visit outside, twenty six children developed measles later. The secondary attack rate of measles is :

66.6%. ***66.6%*** - The **secondary attack rate** is calculated as (number of secondary cases / number of susceptible contacts exposed to the primary case) × 100. - Total children = 100, with 60% vaccinated (60 children), leaving **40 susceptible children**. - The primary case (one child from the village who visited outside) is part of these 40 susceptible children. - After the primary case occurs, the **remaining susceptible contacts** = 40 - 1 = **39 children**. - Number of secondary cases = 26, so secondary attack rate = (26/39) × 100 = **66.67% ≈ 66.6%**. *65.0%* - This option incorrectly uses all 40 susceptible children as the denominator (26/40 × 100 = 65%). - The error lies in **not excluding the primary case** from the denominator when calculating the secondary attack rate. - The primary case cannot be counted among those "at risk" of secondary infection since they already have the disease. *26.0%* - This represents the **overall attack rate** calculated as (26/100) × 100, using the total population as the denominator. - It fails to account for **vaccination status** and does not represent the secondary attack rate among susceptible contacts. - This is epidemiologically incorrect for measuring disease transmission among susceptibles. *16.6%* - This option appears to use an incorrect denominator, possibly 26/156 or another erroneous calculation. - It does not reflect any standard epidemiological rate calculation for this scenario. - The value is too low to represent the true risk among susceptible contacts.

Q: Serial interval is the gap between :

Primary and secondary case. ***Primary and secondary case*** - The **serial interval** is defined as the time between the onset of symptoms in a **primary case** and the onset of symptoms in a **secondary case** infected by the primary case. - It is a crucial epidemiological parameter used to estimate the **reproduction number (R)** of infectious diseases. *Index and primary case* - The **index case** is the first case identified in an outbreak, while the **primary case** is the actual first case to get the disease. These two might not always be the same. - The serial interval specifically links the source of transmission (primary case) to the recipient (secondary case) based on symptom onset. *Introduction of infection and development of maximum infectivity* - This describes the **incubation period** or a phase within it, not the serial interval. - The serial interval measures the time between symptomatic onsets in a transmission chain. *Transmission of infection from patient to another susceptible host* - This describes the event of **actual transmission**, but the serial interval is the time duration between the manifestation of symptoms in the two individuals involved in this transmission. - It focuses on the time between **symptom onset**, not the time of transmission itself.

Q: In a village of 5,000 population, 50 persons suffered from cholera and 10 persons died. What will be the case fatality ratio?

20.0%. ***20.0%*** - The **case fatality ratio (CFR)** is calculated as the number of deaths from a specific disease divided by the number of confirmed cases of that disease, multiplied by 100. - In this scenario, 10 deaths / 50 cases = 0.2, and 0.2 * 100 = **20.0%**. *0.2%* - This value is likely derived from an incorrect calculation, possibly dividing the number of deaths by the total population, which would represent a **mortality rate**, not a case fatality ratio. - The **case fatality ratio** specifically relates deaths to the number of *cases*, not the entire population. *5.0%* - This calculation might be a misinterpretation of the formula or an application of the wrong denominator. - The correct denominator for **case fatality ratio** is the number of **cases**, not the total population or a subset of it unrelated to the disease. *1.0%* - This percentage would result from a different set of numbers for deaths and cases, or an error in calculation. - The **case fatality ratio** is focused on the severity of the disease among those who *contract* it, not the prevalence in the general population.

Q: The amount of previously unrecognized disease that is diagnosed as a result of the screening effort is known as :

Yield. ***Yield*** - The **yield** of a screening program refers to the amount of **previously unrecognized disease** that is identified through the screening effort. - It essentially measures the **productivity** or **effectiveness** of the screening intervention in detecting new cases. *Reliability* - **Reliability** refers to the **consistency** of a measurement or test, meaning it produces the same results under the same conditions. - It does not describe the amount of new disease found but rather the **reproducibility** of the screening process. *Predictive accuracy* - **Predictive accuracy** (positive predictive value or negative predictive value) indicates the probability that a positive or negative test result **truly reflects** the presence or absence of the disease. - While related to screening performance, it's a measure of how accurately the test predicts disease status, not the overall quantity of newly diagnosed disease. *Validity* - **Validity** refers to the extent to which a test measures what it is intended to measure, encompassing both **sensitivity** and **specificity**. - It describes the **accuracy** of the test in correctly identifying diseased and non-diseased individuals, but not the total number of new cases identified in the population.

Q: In disability rates, event type indicators are the following except

Limitation of activity. ***Limitation of activity*** - While related to disability measurement, **limitation of activity** is typically classified as a **chronic disability indicator** or **impact indicator** rather than an event type indicator measured in discrete time units. - Event type indicators usually quantify disability in **specific time units (days)** representing acute episodes or events. - **Limitation of activity** describes a long-term functional status rather than countable discrete events. *Work loss days* - **Work loss days** are a standard **event type indicator** measuring days of work lost due to illness or injury. - This is a specific type of restricted activity day for the employed population. - Quantifies disability impact in discrete, countable time units (days). *Bed disability days* - **Bed disability days** directly measure severe disability events where an individual is confined to bed. - This is a classic **event type indicator** used in national health surveys. - Represents the most severe form of restricted activity days. *Number of days of restricted activity* - **Restricted activity days** are the primary **event type indicator** in disability measurement. - Quantifies days when usual activities are limited due to health conditions. - This is the broadest category of event type indicators, encompassing bed disability days and work loss days.

Q: The detection of sore throat cases in children and their treatment with Benzathine Penicillin in Community Control Programme of Rheumatic Fever/Rheumatic Heart Disease (RF/RHD) constitutes

Primary prevention of RF/RHD. ***Primary prevention of RF/RHD*** - **Early detection and treatment** of streptococcal sore throat prevents the initial episode of **acute rheumatic fever (ARF)**, thus preventing the onset of **rheumatic heart disease (RHD)**. - This intervention targets preventing the disease's **initial occurrence** by eliminating the precipitating cause. *Primordial prevention of RF/RHD* - **Primordial prevention** focuses on preventing the development of **risk factors** in the first place, often through broad social or environmental changes. - This involves strategies like improving **socioeconomic conditions** or **housing sanitation** to reduce the overall burden of streptococcal infections, rather than treating individual cases. *Tertiary prevention of RF/RHD* - **Tertiary prevention** aims to **reduce the impact** of an established disease, minimizing complications and improving quality of life. - For RF/RHD, this would involve managing **existing RHD**, such as through cardiac surgery or long-term medication, to prevent further deterioration or disability. *Secondary prevention of RF/RHD* - **Secondary prevention** involves detecting and treating a disease **early** to prevent its progression or recurrence *after* an initial episode. - In the context of RF/RHD, this would refer to **secondary prophylaxis with penicillin** given to individuals who have already had ARF to prevent subsequent attacks and progression to RHD.

Question 1

Berksonian bias is a selection bias which occurs in

Accepted Answer

Hospital based studies

Answer

Natural exposure studies

Answer

Community based studies

Answer

Laboratory based studies

Question 2

Match the diseases in List-I with their respective incubation periods in List-II and select the correct answer using the code given below:

Accepted Answer

A→1  B→2  C→3  D→4

Answer

A→4  B→3  C→2  D→1

Answer

A→1  B→4  C→3  D→2

Answer

A→3  B→4  C→2  D→1

Question 3

The net reproduction rate of 1 is primarily determined by which of the following demographic rates?

Accepted Answer

Total fertility rate

Answer

Couple protection rate

Answer

Total marital fertility rate

Answer

Age specific marital fertility rate

Question 4

The useful fertility indicator where birth registration statistics do not exist or are inadequate is :

Accepted Answer

Child-woman ratio

Answer

Abortion rate

Answer

Net reproduction rate

Answer

Male-female ratio

Question 5

A village has a total of 100 under-five children. The coverage with measles vaccine in these age groups is 60%. Following the occurrence of a measles case in a child after a visit outside, twenty six children developed measles later. The secondary attack rate of measles is :

Accepted Answer

66.6%

Answer

26.0%

Answer

65.0%

Answer

16.6%

Question 6

Serial interval is the gap between :

Accepted Answer

Primary and secondary case

Answer

Index and primary case

Answer

Introduction of infection and development of maximum infectivity

Answer

Transmission of infection from patient to another susceptible host

Question 7

In a village of 5,000 population, 50 persons suffered from cholera and 10 persons died. What will be the case fatality ratio?

Accepted Answer

20.0%

Answer

0.2%

Answer

5.0%

Answer

1.0%

Question 8

The amount of previously unrecognized disease that is diagnosed as a result of the screening effort is known as :

Accepted Answer

Yield

Answer

Reliability

Answer

Predictive accuracy

Answer

Validity

Question 9

In disability rates, event type indicators are the following except

Accepted Answer

Limitation of activity

Answer

Work loss days

Answer

Bed disability days

Answer

Number of days of restricted activity

Question 10

The detection of sore throat cases in children and their treatment with Benzathine Penicillin in Community Control Programme of Rheumatic Fever/Rheumatic Heart Disease (RF/RHD) constitutes

Accepted Answer

Primary prevention of RF/RHD

Answer

Primordial prevention of RF/RHD

Answer

Tertiary prevention of RF/RHD

Answer

Secondary prevention of RF/RHD

Epidemiology — MCQs

Epidemiology — MCQs

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