APPLIED EPIDEMIOLOGY AND BIOSTATISTICS MIDTERM EXAM
COMPLETE QUESTIONS AND VERIFIED ANSWERS LATEST VERSION 2026
1. What is epidemiology? The study of the distribution and determinants of
health-related states or events in specified populations and the application of
this study to control health problems.
2. What are the three main objectives of epidemiology? To describe the
distribution of disease, to identify etiological factors, and to provide data for
prevention and control programs.
3. Define prevalence. The proportion of a population that has a disease or
condition at a specific point in time or during a specified period.
4. Define incidence. The number of new cases of a disease that occur in a
defined population during a specified time period.
5. What is the formula for prevalence? Prevalence = (Number of existing
cases / Total population at risk) × 100 or × 1,000
6. What is the formula for incidence rate? Incidence rate = (Number of new
cases / Person-time at risk) × multiplier (often × 1,000 or × 100,000)
7. What is the difference between incidence and prevalence? Incidence
measures new cases occurring over time, while prevalence measures all existing
cases at a point in time.
8. What is cumulative incidence? The proportion of people who develop
disease during a specified period among those initially disease-free. Also called
incidence proportion or attack rate.
9. What is person-time? A measure that combines the number of people in a
study with the time each person is observed, expressed as person-years, person-
months, etc.
10. What is an epidemic? The occurrence of disease clearly in excess of
normal expectancy in a community or region.
,11. What is a pandemic? An epidemic that has spread over several countries or
continents, usually affecting a large number of people.
12. What is endemic disease? The constant presence of a disease or infectious
agent within a given geographic area or population.
13. What is the epidemiologic triad? A model consisting of three components:
agent, host, and environment, which interact to produce disease.
14. What is the web of causation? A model that recognizes multiple factors
(biological, social, environmental) interact in complex ways to cause disease.
15. What are the five modes of disease transmission? Direct contact, indirect
contact, droplet, airborne, and vector-borne transmission.
16. Define primary prevention. Measures to prevent disease before it occurs,
such as immunization, health education, and environmental modifications.
17. Define secondary prevention. Early detection and treatment of disease to
prevent progression, such as screening programs.
18. Define tertiary prevention. Measures to reduce complications and
disabilities from established disease, such as rehabilitation programs.
19. What is a risk factor? An attribute or exposure that is associated with an
increased probability of a specified outcome, such as disease.
20. What is a protective factor? An attribute or exposure associated with
decreased probability of disease.
21. What is screening? The systematic application of a test to identify
individuals at sufficient risk of a disorder to benefit from further investigation or
direct preventive action.
22. What are the criteria for a good screening test? The disease should be
serious, have early detectable stage, effective treatment available, test should be
acceptable, safe, valid, and cost-effective.
23. What is the natural history of disease? The progression of disease from
onset through recovery, disability, or death without medical intervention.
24. What is the latency period? The time between exposure to an agent and
the onset of disease.
, 25. What is the incubation period? The time between infection and the
appearance of symptoms in infectious diseases.
26. What is herd immunity? When a sufficient proportion of a population is
immune to an infectious disease, providing indirect protection to non-immune
individuals.
27. What is R0 (basic reproduction number)? The average number of
secondary cases generated by one infected individual in a completely
susceptible population.
28. What is surveillance in epidemiology? The ongoing systematic collection,
analysis, and interpretation of health data for planning, implementation, and
evaluation of public health practice.
29. What is passive surveillance? Surveillance based on reports submitted by
healthcare providers, laboratories, or other entities without active solicitation.
30. What is active surveillance? Surveillance involving regular outreach to
healthcare providers or laboratories to gather information.
31. What is an outbreak investigation? A systematic process to identify the
source and extent of disease transmission and implement control measures.
32. What are the steps in an outbreak investigation? Prepare, verify
diagnosis, establish case definition, find cases, perform descriptive
epidemiology, develop hypotheses, test hypotheses, implement control
measures, and communicate findings.
33. What is a case definition? A set of standard criteria for deciding whether a
person has a particular disease or health condition.
34. What is a confirmed case? A case that meets the clinical case definition
and has laboratory confirmation.
35. What is a probable case? A case that meets the clinical case definition but
lacks laboratory confirmation.
36. What is a suspect case? A case that is compatible with the case definition
but has incomplete information.
37. What is an index case? The first case in a family or defined group to come
to the attention of the investigator.
38. What is a primary case? The first case in an outbreak or epidemic.
COMPLETE QUESTIONS AND VERIFIED ANSWERS LATEST VERSION 2026
1. What is epidemiology? The study of the distribution and determinants of
health-related states or events in specified populations and the application of
this study to control health problems.
2. What are the three main objectives of epidemiology? To describe the
distribution of disease, to identify etiological factors, and to provide data for
prevention and control programs.
3. Define prevalence. The proportion of a population that has a disease or
condition at a specific point in time or during a specified period.
4. Define incidence. The number of new cases of a disease that occur in a
defined population during a specified time period.
5. What is the formula for prevalence? Prevalence = (Number of existing
cases / Total population at risk) × 100 or × 1,000
6. What is the formula for incidence rate? Incidence rate = (Number of new
cases / Person-time at risk) × multiplier (often × 1,000 or × 100,000)
7. What is the difference between incidence and prevalence? Incidence
measures new cases occurring over time, while prevalence measures all existing
cases at a point in time.
8. What is cumulative incidence? The proportion of people who develop
disease during a specified period among those initially disease-free. Also called
incidence proportion or attack rate.
9. What is person-time? A measure that combines the number of people in a
study with the time each person is observed, expressed as person-years, person-
months, etc.
10. What is an epidemic? The occurrence of disease clearly in excess of
normal expectancy in a community or region.
,11. What is a pandemic? An epidemic that has spread over several countries or
continents, usually affecting a large number of people.
12. What is endemic disease? The constant presence of a disease or infectious
agent within a given geographic area or population.
13. What is the epidemiologic triad? A model consisting of three components:
agent, host, and environment, which interact to produce disease.
14. What is the web of causation? A model that recognizes multiple factors
(biological, social, environmental) interact in complex ways to cause disease.
15. What are the five modes of disease transmission? Direct contact, indirect
contact, droplet, airborne, and vector-borne transmission.
16. Define primary prevention. Measures to prevent disease before it occurs,
such as immunization, health education, and environmental modifications.
17. Define secondary prevention. Early detection and treatment of disease to
prevent progression, such as screening programs.
18. Define tertiary prevention. Measures to reduce complications and
disabilities from established disease, such as rehabilitation programs.
19. What is a risk factor? An attribute or exposure that is associated with an
increased probability of a specified outcome, such as disease.
20. What is a protective factor? An attribute or exposure associated with
decreased probability of disease.
21. What is screening? The systematic application of a test to identify
individuals at sufficient risk of a disorder to benefit from further investigation or
direct preventive action.
22. What are the criteria for a good screening test? The disease should be
serious, have early detectable stage, effective treatment available, test should be
acceptable, safe, valid, and cost-effective.
23. What is the natural history of disease? The progression of disease from
onset through recovery, disability, or death without medical intervention.
24. What is the latency period? The time between exposure to an agent and
the onset of disease.
, 25. What is the incubation period? The time between infection and the
appearance of symptoms in infectious diseases.
26. What is herd immunity? When a sufficient proportion of a population is
immune to an infectious disease, providing indirect protection to non-immune
individuals.
27. What is R0 (basic reproduction number)? The average number of
secondary cases generated by one infected individual in a completely
susceptible population.
28. What is surveillance in epidemiology? The ongoing systematic collection,
analysis, and interpretation of health data for planning, implementation, and
evaluation of public health practice.
29. What is passive surveillance? Surveillance based on reports submitted by
healthcare providers, laboratories, or other entities without active solicitation.
30. What is active surveillance? Surveillance involving regular outreach to
healthcare providers or laboratories to gather information.
31. What is an outbreak investigation? A systematic process to identify the
source and extent of disease transmission and implement control measures.
32. What are the steps in an outbreak investigation? Prepare, verify
diagnosis, establish case definition, find cases, perform descriptive
epidemiology, develop hypotheses, test hypotheses, implement control
measures, and communicate findings.
33. What is a case definition? A set of standard criteria for deciding whether a
person has a particular disease or health condition.
34. What is a confirmed case? A case that meets the clinical case definition
and has laboratory confirmation.
35. What is a probable case? A case that meets the clinical case definition but
lacks laboratory confirmation.
36. What is a suspect case? A case that is compatible with the case definition
but has incomplete information.
37. What is an index case? The first case in a family or defined group to come
to the attention of the investigator.
38. What is a primary case? The first case in an outbreak or epidemic.
