UPSC-CMS 2009 - Community Medicine PYQs Practice Questions

Q: For a screening test, 90% specificity means that 90% of non-diseased persons will give a

True negative result. ***True negative result*** - **Specificity** is defined as the proportion of **true negatives** among individuals **without the disease**. - A 90% specificity means that 90% of healthy individuals will correctly test negative for the disease. *False negative result* - A **false negative** occurs when a diseased person tests negative, which is related to the concept of **sensitivity**, not specificity. - This would imply missing actual cases of the disease. *True positive result* - A **true positive** occurs when a diseased person tests positive, which is also related to **sensitivity**. - This indicates accurate detection of the disease in affected individuals. *False positive result* - A **false positive** occurs when a non-diseased person inappropriately tests positive. - If 90% of non-diseased persons give a negative result (true negative), then 10% would give a **false positive result**. [Practice more Community Medicine PYQs on OnCourse]

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. [Practice more Community Medicine PYQs on OnCourse]

Q: According to International Health Regulations, there is no risk of spread of yellow fever if the Aedes aegypti index is kept at

below 1%. ***below 1%*** - The **International Health Regulations (IHR)** specify that a **house index** (percentage of houses infested with *Aedes aegypti* larvae) of **below 1%** is considered sufficient to prevent the spread of yellow fever. - Maintaining this low index is crucial for controlling potential outbreaks in endemic or receptive areas. *2-4%* - An *Aedes aegypti* index in this range (2-4%) indicates a **moderate risk** of yellow fever transmission, as the vector population is still significant enough to facilitate spread. - This level is **above the recommended threshold** for effective prevention according to IHR. *5-7%* - An index between 5-7% signifies an **elevated risk** of yellow fever transmission, indicating a substantial presence of the vector population. - At this level, there is a **high probability** of ongoing or impending disease outbreaks. *8-10%* - An *Aedes aegypti* index of 8-10% represents a **very high risk** of yellow fever spread, suggesting an widespread vector presence. - This range indicates a **strong potential for rapid and extensive disease transmission**. [Practice more Community Medicine PYQs on OnCourse]

Q: During the process of chlorination of water, the disinfecting action of chlorine is due to the formation of

Hypochlorous acid and hypochlorite ions. ***Hypochlorous acid and hypochlorite ions*** - When **chlorine gas** (Cl2) is added to water, it rapidly reacts to form **hypochlorous acid (HOCl)** and **hydrochloric acid (HCl)**. - Hypochlorous acid then partially dissociates into **hypochlorite ions (OCl-)** depending on the pH of the water; both HOCl and OCl- are potent disinfectants, with HOCl being 80-100 times more effective. *Chlorine gas only* - While chlorine gas is the starting material for chlorination, it is not the primary disinfectant in water. - Chlorine gas reacts with water to form other active disinfectant compounds; it does not directly act as a disinfectant at significant levels in water treatment. *Hydrochloric acid only* - **Hydrochloric acid (HCl)** is a byproduct of the reaction of chlorine with water, but it is not the active disinfecting agent. - HCl contributes to the lowering of pH but does not possess the strong antimicrobial properties of hypochlorous acid or hypochlorite ions. *Hypochlorous acid only* - **Hypochlorous acid (HOCl)** is indeed a very strong disinfectant and a critical component of water chlorination. - However, in typical water treatment pH ranges, a significant proportion of HOCl also dissociates into **hypochlorite ions (OCl-)**, which also contribute to the disinfecting action, making the combined effect the primary mechanism. [Practice more Community Medicine PYQs on OnCourse]

Q: Kata thermometer is used for recording :

Low air velocities. ***Low air velocities*** - A **Kata thermometer** is a specialized alcohol thermometer designed to measure **cooling power** and **air velocity** in various environments. - It works by being heated to a specific temperature and then measuring the time it takes to cool down, which is influenced by air movement. *Relative humidity of the air* - **Relative humidity** is typically measured using a **psychrometer** (a wet-bulb and dry-bulb thermometer) or a **hygrometer**. - The Kata thermometer does not directly measure humidity; rather, humidity can indirectly influence its cooling rate. *Mean radiant temperature* - **Mean radiant temperature** is measured using a **globe thermometer**, which uses a temperature sensor inside a black globe. - The Kata thermometer is not designed for this purpose, as it primarily assesses air movement and cooling power. *Maximum and minimum temperature* - **Maximum and minimum temperatures** are typically recorded by a **Six's thermometer** or conventional mercury/alcohol thermometers. - While a Kata thermometer has a temperature scale, its primary use is not for simple maximum/minimum readings but for measuring air velocity and cooling. [Practice more Community Medicine PYQs on OnCourse]

Question 1

For a screening test, 90% specificity means that 90% of non-diseased persons will give a

Accepted Answer

True negative result

Answer

False negative result

Answer

True positive result

Answer

False positive result

Question 2

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 3

According to International Health Regulations, there is no risk of spread of yellow fever if the Aedes aegypti index is kept at

Accepted Answer

below 1%

Answer

2-4%

Answer

5-7%

Answer

8-10%

Question 4

During the process of chlorination of water, the disinfecting action of chlorine is due to the formation of

Accepted Answer

Hypochlorous acid and hypochlorite ions

Answer

Chlorine gas only

Answer

Hydrochloric acid only

Answer

Hypochlorous acid only

Question 5

Kata thermometer is used for recording :

Accepted Answer

Low air velocities

Answer

Relative humidity of the air

Answer

Mean radiant temperature

Answer

Maximum and minimum temperature

Question 6

Match List-I with List-II and select the correct answer using the code given below the Lists:

Accepted Answer

A→1  B→2  C→4  D→3

Answer

A→1  B→4  C→2  D→3

Answer

A→4  B→3  C→2  D→1

Answer

A→1  B→2  C→3  D→4

Question 7

Consider the following :

1. Land filling for source reduction.
2. Vaccination of pigs in the risk area.
3. Immunization of children in risk area. Which of the above are the recommended control strategies for Japanese Encephalitis ?

Accepted Answer

2 and 3 only

Answer

1 only

Answer

1, 2 and 3

Answer

1 and 2 only

Question 8

In a community with one lakh population, 20,000 slides were examined in a particular year. Out of these 100 were positive for malarial parasite. What is the Annual Parasite Incidence (API) in this community ?

Accepted Answer

1

Answer

2

Answer

0.5

Answer

5

Question 9

Amniocentesis in early pregnancy for genetic disorders is a kind of

Accepted Answer

primary prevention

Answer

secondary prevention

Answer

tertiary prevention

Answer

primordial prevention

Question 10

Which one of the following is a correct combination regarding Indian population?

Accepted Answer

Blood group O 40%; Rh negative 7%

Answer

Blood group AB 20%; Rh negative 15%

Answer

Blood group A 40%; Rh positive 80%

Answer

Blood group B 33%; Rh positive 99%

UPSC-CMS 2009 — Community Medicine