Epidemiology 2 EXAM QUESTIONS AND CORRECT DETAILED ANSWERS WITH
RATIONALES (VERIFIED ANSWERS) ALREADY GRADED A+ NEWEST VERSION
Experimental Vs Observational - (answer)- Experimental: manipulation of study factor; and randomly
assigns subjects to treatment and control group
- Observational: no manipulation of study factor nor randomization
Case Reports - (answer)- Observational study design
- Descriptive
- Single Reports (unusual cases)
Case Series - (answer)- Observational study design
- Descriptive
- Multiple unusual cases
Cross-sectional - (answer)- Observational study design
- Descriptive
- Surveys the population to estimate the prevalence of a disease
- Exposure and disease measures obtained:
at the individual level and simultaneously
- Single period of observation
Applications of Cross-Sectional Studies - (answer)- can describe the magnitude and distribution of a
health problem
- repeated cross-sectional surveys can be used to examine trends in disease or risk factors that vary over
time
- to evaluate and compare trends in health and disease
- Planning, provision, and evaluation of health services (intervention)
- To identify problems for analytic studies and suggest areas for investigation (hypothesis generating)
,Epidemiology 2 EXAM QUESTIONS AND CORRECT DETAILED ANSWERS WITH
RATIONALES (VERIFIED ANSWERS) ALREADY GRADED A+ NEWEST VERSION
Cross-sectional: Advantages and Disadvantages - (answer)- Advantages: generalizability, conducted in
relatively short period of time, low cost
- Disadvantage: limited usefulness of inferring disease etiology, do NOT provide incidence data, cannot
study low prevalence diseases, cannot determine temporality of exposure and disease (i.e. whether
exposure or disease come first)
Ecologic - (answer)- Observational study design
- Analytic
- Unit of analysis is the GROUP, not the individual
- Generally makes use of secondary data collected by government, some other agency, or investigators
(census tract)
- The level of exposure for each individual in the unit being studied is unknown
Types of Ecologic Studies - (answer)- Ecologic comparison study - involves an assessment of the
correlation between exposure rates and disease rates among different groups over the same time
period
- Ecologic trend (time series) study - involves correlation of changes in exposure with changes in disease
over time within the same community, country, or other aggregate unit
Ecologic Fallacy - (answer)- Observations made at the group level may not represent the exposure-
disease relationship at the individual level
- Ecologic fallacy occurs when incorrect inferences about the individual are made from group level data
- The conclusions obtained from an ecologic study may be the reverse of those from a study that collects
data on individual subjects
Example of Ecologic Fallacy - (answer)- An ecologic study examines 10 individuals who go into the sun
- 7 persons have sunburned foreheads
- 6 persons wore hats
- Results suggest that there is an association between the exposure (wearing hats) and disease
(sunburn)
, Epidemiology 2 EXAM QUESTIONS AND CORRECT DETAILED ANSWERS WITH
RATIONALES (VERIFIED ANSWERS) ALREADY GRADED A+ NEWEST VERSION
- the conclusion based on the association between hats and sunburns at the group level was incorrect
Applications of Ecologic Studies - (answer)- Test specific etiologic hypotheses
- Develop new etiologic hypotheses
- Suggest mechanisms of causation
- Identify new methods for disease prevention
Ecologic Studies: Advantages and Disadvantages - (answer)- Advantages: quick, simple, inexpensive,
good approach for generating hypotheses when a disease is of unknown etiology
- Disadvantages: ecological fallacy, imprecise measurement of exposure and disease
Case-control - (answer)- Observational study design
- Analytic
- Type of design that compares persons who have a disease (cases) with those who are free from the
disease (controls)
- This design explores whether differences between cases and controls result from exposures to risk
factors
Case-control Cont. - (answer)- A single point of observation
- Unit of observation and the unit of analysis are the individual
- exposure is determined retrospectively
- does not directly provide incidence data
- data collection typically involves both primary and secondary sources
Selection of Cases in Case-control - (answer)Two Tasks:
- Defining a case conceptually:
standard diagnostic criteria, severity of the disease
- Identifying a case operationally
RATIONALES (VERIFIED ANSWERS) ALREADY GRADED A+ NEWEST VERSION
Experimental Vs Observational - (answer)- Experimental: manipulation of study factor; and randomly
assigns subjects to treatment and control group
- Observational: no manipulation of study factor nor randomization
Case Reports - (answer)- Observational study design
- Descriptive
- Single Reports (unusual cases)
Case Series - (answer)- Observational study design
- Descriptive
- Multiple unusual cases
Cross-sectional - (answer)- Observational study design
- Descriptive
- Surveys the population to estimate the prevalence of a disease
- Exposure and disease measures obtained:
at the individual level and simultaneously
- Single period of observation
Applications of Cross-Sectional Studies - (answer)- can describe the magnitude and distribution of a
health problem
- repeated cross-sectional surveys can be used to examine trends in disease or risk factors that vary over
time
- to evaluate and compare trends in health and disease
- Planning, provision, and evaluation of health services (intervention)
- To identify problems for analytic studies and suggest areas for investigation (hypothesis generating)
,Epidemiology 2 EXAM QUESTIONS AND CORRECT DETAILED ANSWERS WITH
RATIONALES (VERIFIED ANSWERS) ALREADY GRADED A+ NEWEST VERSION
Cross-sectional: Advantages and Disadvantages - (answer)- Advantages: generalizability, conducted in
relatively short period of time, low cost
- Disadvantage: limited usefulness of inferring disease etiology, do NOT provide incidence data, cannot
study low prevalence diseases, cannot determine temporality of exposure and disease (i.e. whether
exposure or disease come first)
Ecologic - (answer)- Observational study design
- Analytic
- Unit of analysis is the GROUP, not the individual
- Generally makes use of secondary data collected by government, some other agency, or investigators
(census tract)
- The level of exposure for each individual in the unit being studied is unknown
Types of Ecologic Studies - (answer)- Ecologic comparison study - involves an assessment of the
correlation between exposure rates and disease rates among different groups over the same time
period
- Ecologic trend (time series) study - involves correlation of changes in exposure with changes in disease
over time within the same community, country, or other aggregate unit
Ecologic Fallacy - (answer)- Observations made at the group level may not represent the exposure-
disease relationship at the individual level
- Ecologic fallacy occurs when incorrect inferences about the individual are made from group level data
- The conclusions obtained from an ecologic study may be the reverse of those from a study that collects
data on individual subjects
Example of Ecologic Fallacy - (answer)- An ecologic study examines 10 individuals who go into the sun
- 7 persons have sunburned foreheads
- 6 persons wore hats
- Results suggest that there is an association between the exposure (wearing hats) and disease
(sunburn)
, Epidemiology 2 EXAM QUESTIONS AND CORRECT DETAILED ANSWERS WITH
RATIONALES (VERIFIED ANSWERS) ALREADY GRADED A+ NEWEST VERSION
- the conclusion based on the association between hats and sunburns at the group level was incorrect
Applications of Ecologic Studies - (answer)- Test specific etiologic hypotheses
- Develop new etiologic hypotheses
- Suggest mechanisms of causation
- Identify new methods for disease prevention
Ecologic Studies: Advantages and Disadvantages - (answer)- Advantages: quick, simple, inexpensive,
good approach for generating hypotheses when a disease is of unknown etiology
- Disadvantages: ecological fallacy, imprecise measurement of exposure and disease
Case-control - (answer)- Observational study design
- Analytic
- Type of design that compares persons who have a disease (cases) with those who are free from the
disease (controls)
- This design explores whether differences between cases and controls result from exposures to risk
factors
Case-control Cont. - (answer)- A single point of observation
- Unit of observation and the unit of analysis are the individual
- exposure is determined retrospectively
- does not directly provide incidence data
- data collection typically involves both primary and secondary sources
Selection of Cases in Case-control - (answer)Two Tasks:
- Defining a case conceptually:
standard diagnostic criteria, severity of the disease
- Identifying a case operationally
