Which of the following is NOT one of Bradford Hill's criteria for causation?
What is the most common mode of transmission of HIV?
Multiphasic screening means-
What is the definition of a reservoir in the context of infectious diseases?
What is a key benefit of Randomized Controlled Trials (RCTs) in clinical research?
Most commonly used blinding technique in epidemiological studies?
Human, animal, fomite or objects from which infective organism enters the host is called?
Which one of the following is NOT a utilization rate?
Which of the following statements is true regarding a combined prospective-retrospective study?
What is the definition of Population Attributable Risk?
NEET-PG 2015 - Community Medicine NEET-PG Practice Questions and MCQs
Question 11: Which of the following is NOT one of Bradford Hill's criteria for causation?
- A. Consistency of association
- B. Specificity of association
- C. Strength of association
- D. Absence of temporal relationship (Correct Answer)
Explanation: ***Absence of temporal relationship*** - Bradford Hill's criteria include **temporality** (temporal relationship), which states that the cause must precede the effect in time. - The criterion is the **presence** of a temporal relationship, not its absence. - "Absence of temporal relationship" is therefore NOT one of Bradford Hill's criteria—it is the opposite of what the criterion requires. - This is the correct answer to this "NOT" question. *Strength of association* - This **IS** one of Bradford Hill's criteria. - It refers to the **magnitude of the association** between exposure and outcome (measured by relative risk, odds ratio, etc.). - A stronger association provides more evidence for causality. *Consistency of association* - This **IS** one of Bradford Hill's criteria. - It means the association is observed **repeatedly** across different studies, populations, settings, and times. - Consistent replication strengthens the causal argument. *Specificity of association* - This **IS** one of Bradford Hill's criteria. - It suggests that a specific exposure leads to a specific outcome with limited alternative explanations. - While supportive of causation, Hill noted this criterion is less essential as many exposures have multiple effects.
Question 12: What is the most common mode of transmission of HIV?
- A. Occupational exposure (needle stick injury)
- B. Perinatal transmission (mother to child)
- C. Sexual contact (Correct Answer)
- D. Transmission via blood and blood products
Explanation: ***Sexual contact*** - **Unprotected sexual intercourse**, both heterosexual and homosexual, is overwhelmingly the most common way HIV is transmitted globally. - The virus can be exchanged through **bodily fluids** such as semen, vaginal fluids, and rectal fluids during sexual activity. - Accounts for approximately **80% of new HIV infections** worldwide. *Occupational exposure (needle stick injury)* - While a recognised mode of transmission, **needle stick injuries** account for a very small percentage of total HIV infections, primarily affecting healthcare workers. - The risk of transmission per exposure is relatively low (approximately **0.3%**), especially compared to sexual contact. *Perinatal transmission (mother to child)* - **Mother-to-child transmission** can occur during pregnancy, childbirth, or breastfeeding. - Although significant, especially in resource-limited settings, global efforts and **PMTCT programs** have resulted in a significant reduction in this type of transmission. *Transmission via blood and blood products* - This mode was once a major concern but is now extremely rare in countries with robust **blood screening programs**. - While sharing contaminated needles among **intravenous drug users** remains a risk, transfusion-related HIV is largely controlled.
Question 13: Multiphasic screening means-
- A. Application of two or more screening tests in combination at different geographical areas
- B. Application of separate screening tests for different diseases
- C. Application of two or more screening tests in combination at one time (Correct Answer)
- D. Application of two or more screening tests in combination at different times
Explanation: ***Application of two or more screening tests in combination at one time*** - **Multiphasic screening** involves performing several screening tests simultaneously during a single screening session. - This approach aims to detect multiple diseases or risk factors efficiently within a single visit or examination. *Application of two or more screening tests in combination at different times* - This describes repeated screening or sequential screening, where tests are administered over a period, not the immediate, combined approach of multiphasic screening. - **Multiphasic screening** specifically refers to the concurrent application of multiple tests, not their staggered use. *Application of two or more screening tests in combination at different geographical areas* - This concept relates more to large-scale public health programs or epidemiological studies across regions, rather than the definition of multiphasic screening itself. - Geographical variation is not a defining characteristic of multiphasic screening. *Application of separate screening tests for different diseases* - While multiphasic screening indeed uses separate tests for different diseases, the key aspect is their **simultaneous application** at one time to a single individual, which this option omits. - This option describes the general nature of screening for various conditions but misses the crucial element of combination and timing.
Question 14: What is the definition of a reservoir in the context of infectious diseases?
- A. Person, animal or object from which infectious agent is transmitted to host
- B. Person, animal or substance in which infectious agent lives and multiplies (Correct Answer)
- C. Person or animal in which infectious agent causes a disease
- D. Person or animal that transmits the infectious agent mechanically
Explanation: ***Person, animal or substance in which infectious agent lives and multiplies*** - A **reservoir** is the natural habitat where an **infectious agent** normally lives and multiplies, and from which it can be transmitted to a susceptible host. - This definition emphasizes residence and replication, not necessarily direct transmission to a new host or causation of disease in the reservoir itself. - Examples include humans (e.g., typhoid carriers), animals (e.g., rodents for plague), and environmental sources (e.g., soil for tetanus). *Person, animal or object from which infectious agent is transmitted to host* - This option describes a **source of infection**, which can be a reservoir but isn't always. A source is where a host acquires the infection, but not necessarily where the pathogen multiplies. - An object (fomite) can be a source of infection, but it's rarely a reservoir because pathogens generally do not live and multiply there for extended periods. *Person or animal in which infectious agent causes a disease* - This describes a **diseased host** or a **case**, not necessarily a reservoir. A reservoir may or may not experience disease from the pathogen it harbors. - For example, a **carrier** can be a reservoir without showing symptoms of disease. *Person or animal that transmits the infectious agent mechanically* - This describes a **vector**, particularly a mechanical vector (e.g., flies carrying pathogens on their body). - Unlike a reservoir, a vector does not provide a habitat where the pathogen lives and multiplies; it merely transports it from one location to another.
Question 15: What is a key benefit of Randomized Controlled Trials (RCTs) in clinical research?
- A. They can be conducted more quickly than other study types.
- B. They minimize selection bias. (Correct Answer)
- C. They are ideal for studying rare diseases.
- D. They are generally less expensive than other study types.
Explanation: ***They minimize selection bias.*** - **Randomization** in RCTs ensures that participants have an equal chance of being assigned to any of the treatment groups, thereby balancing potential **confounding factors** across groups. - This balance helps to ensure that any observed differences in outcomes between groups are more likely due to the intervention being studied rather than pre-existing differences among participants, thus minimizing **selection bias**. *They can be conducted more quickly than other study types.* - RCTs often require **extensive planning**, recruitment, and follow-up periods, making them one of the **most time-consuming** study designs. - The need for sufficient **power** to detect meaningful differences often translates into longer study durations. *They are ideal for studying rare diseases.* - Due to the requirement for **large sample sizes** to demonstrate statistical significance, RCTs are **not practical** for diseases with low prevalence. - Recruiting enough participants with a rare disease for an RCT can be extremely challenging and often **unfeasible**. *They are generally less expensive than other study types.* - RCTs are typically among the **most expensive** study designs because they involve extensive participant recruitment, intervention administration, data collection, and long-term follow-up. - The costs associated with staff, resources, and monitoring for ethical compliance contribute to their **high financial burden**.
Question 16: Most commonly used blinding technique in epidemiological studies?
- A. None of the options
- B. Single blinding
- C. Double blinding (Correct Answer)
- D. Triple blinding
Explanation: ***Double blinding*** - In **double blinding**, neither the **participants** nor the **researchers** administering the intervention and collecting data know who is in the treatment group versus the control group. - This method is widely used to prevent **observer bias** from the researchers and **participant bias** (e.g., placebo effect) from the subjects, thereby strengthening the study's internal validity. *Single blinding* - In **single blinding**, only the **participants** are unaware of their assignment to either the treatment or control group. - While it helps reduce participant bias, the **researchers' knowledge** of group assignments can still introduce **observer bias**, making it less rigorous than double blinding. *Triple blinding* - **Triple blinding** extends double blinding by ensuring that the **data analysts** are also unaware of the participant group assignments. - This technique further minimizes bias in the **interpretation and analysis of results**, but it is less commonly implemented due to its complexity and increased logistical challenges compared to double blinding. *None of the options* - This option is incorrect because **blinding techniques** are fundamental tools in epidemiological studies and clinical trials to ensure the objectivity and reliability of research findings. - **Blinding** helps eliminate conscious and unconscious biases that could otherwise influence study outcomes.
Question 17: Human, animal, fomite or objects from which infective organism enters the host is called?
- A. Infective Reservoir
- B. Infective Carrier
- C. None of the above
- D. Source of infection (Correct Answer)
Explanation: ***Source of infection*** - The **source of infection** refers to the person, animal, object, or substance from which an infectious agent passes immediately to a host. - This can include humans, animals, fomites, or contaminated objects that directly transmit the infectious organism. - This is the proximate source from which the agent enters the host. *Infective Reservoir* - An **infective reservoir** is the long-term habitat where an infectious agent normally lives, grows, and multiplies. - The reservoir can be human, animal, plant, soil, or inanimate matter where the agent is normally found. - While a reservoir can be a source, the source is specifically the immediate point from which transmission occurs. *Infective Carrier* - An **infective carrier** is an infected person or animal that harbors a specific infectious agent without showing clinical symptoms but can transmit it to others. - A carrier is a type of source (when transmission occurs from them), but the term "source" is broader, encompassing inanimate objects and fomites as well. *None of the above* - This option is incorrect because **Source of infection** accurately describes the concept presented in the question.
Question 18: Which one of the following is NOT a utilization rate?
- A. Population bed ratio (Correct Answer)
- B. Bed occupancy rate
- C. Bed turnover ratio
- D. Average length of stay
Explanation: ***Population bed ratio*** - The **population bed ratio** indicates the number of available beds per unit of population, reflecting healthcare **resource availability** rather than resource utilization. - It is a measure of healthcare capacity and access, not how intensively those beds are being used. *Bed occupancy rate* - The **bed occupancy rate** measures the proportion of available hospital beds that are occupied over a given period, directly indicating the **utilization** of bed resources. - A higher rate suggests more efficient use of beds, while a lower rate may indicate underutilization or excess capacity. *Bed turnover ratio* - The **bed turnover ratio** calculates the number of patients discharged per bed over a specific period, reflecting how frequently beds are being used and re-used. - It indicates the **efficiency** with which beds are being utilized and cleared for new patients. *Average length of stay* - The **average length of stay (ALOS)** represents the average number of days a patient remains hospitalized, which directly relates to the **duration of bed utilization** per patient. - A shorter ALOS can indicate more efficient use of beds, while a longer ALOS may suggest higher resource consumption per patient.
Question 19: Which of the following statements is true regarding a combined prospective-retrospective study?
- A. Only prospective follow-up from current time point
- B. Retrospective identification of cohort followed by prospective follow-up (Correct Answer)
- C. Cross-sectional assessment at a single time point
- D. Only retrospective data collection from past records
Explanation: ***Retrospective identification of cohort followed by prospective follow-up*** - This correctly describes a **combined prospective-retrospective study** (also called an **ambispective or historical prospective study**) - The study begins by **retrospectively identifying a cohort** from past records (e.g., employees exposed to a chemical 10 years ago) - **Past exposure data is collected retrospectively** from existing records - The identified cohort is then **followed forward prospectively** from the current time point to observe future outcomes - This approach combines the **efficiency of retrospective data collection** with the **rigor of prospective follow-up** *Only prospective follow-up from current time point* - The word **"only"** is the critical error - it excludes the retrospective component - This describes a **purely prospective cohort study**, not a combined study - A combined study must include **both retrospective and prospective elements** *Only retrospective data collection from past records* - This describes a **purely retrospective study** (case-control or retrospective cohort) - It lacks the prospective follow-up component essential to a combined study *Cross-sectional assessment at a single time point* - This defines a **cross-sectional study** that provides a snapshot at one moment - It involves neither retrospective cohort identification nor prospective follow-up
Question 20: What is the definition of Population Attributable Risk?
- A. The difference between incidence in population and incidence in exposed.
- B. The difference between incidence in population and incidence in non-exposed. (Correct Answer)
- C. The difference between incidence in population and incidence in non-exposed compared with incidence in exposed.
- D. The difference between incidence in exposed and incidence in non-exposed.
Explanation: ***Correct: The difference between incidence in population and incidence in non-exposed.*** - **Population Attributable Risk (PAR)** quantifies the excess incidence of disease in the total population that is attributable to a specific exposure. - Formula: **PAR = Incidence in total population - Incidence in unexposed** - It represents the amount of disease burden that would be eliminated from the entire population if the exposure were completely removed. - PAR accounts for both the strength of association and the prevalence of exposure in the population. *Incorrect: The difference between incidence in population and incidence in exposed.* - This formula (I(population) - I(exposed)) does not correctly capture PAR. - This calculation does not isolate the portion of disease attributable to the exposure across the entire population. - It fails to provide meaningful information about attributable risk. *Incorrect: The difference between incidence in population and incidence in non-exposed compared with incidence in exposed.* - This option introduces unnecessary complexity and is not the standard definition of PAR. - PAR is a simple difference, not a comparative ratio involving exposed individuals. - This description confuses PAR with other epidemiological measures. *Incorrect: The difference between incidence in exposed and incidence in non-exposed.* - This describes **Attributable Risk (AR)** or **Risk Difference (RD)**, not Population Attributable Risk. - Formula: **AR = I(exposed) - I(unexposed)** - AR measures excess risk in the exposed group only, without considering the prevalence of exposure in the total population. - PAR differs from AR by accounting for how common the exposure is in the population.