EPIDEMIOLOGICAL STUDIES I Flashcards
Descriptive vs Analytical: distribution of health-related states Describes More exploratory Profiles characteristics of groups
Descriptive
Descriptive vs Analytical:
Focuses on “what”
Assumes no hypothesis (only describes; only generate hypothesis; no assuming)
No comparison between groups over time
Descriptive
Descriptive vs Analytical: determinants of the health related states Explains More explanatory Analyzes why group has characteristics
Analytical
Descriptive vs Analytical:
Focuses on “why”
Assumes hypothesis (comparison of groups)
Comparison between groups over time; already testing a certain hypothesis by comparing
Analytical
Study of amount or occurrence of disease; helps in giving a detailed description of the health status of population
Its distribution within the population; aids in recognition of patterns or trends
For the purpose of identifying non-random variation in disease occurrence
Descriptive Study
1st step in risk factor determination
Issues and problems are identified and is served as an area for further investigation
Data leads to formulation of research hypothesis
Descriptive Study
Wherein generated hypothesis can be tested using analytical studies
Sources of data: data are routinely collected
Examples: census, vital registries, clinical records, employment health examination
Uses of Descriptive Studies:
describe patterns of disease occurrence
Trend analysis
Uses of Descriptive Studies:
efficient allocation of resources
Health promotion and prevention programs for identified groups
Health care planning
Uses of Descriptive Studies:
formulation of research questions & hypothesis
1st step in risk factor determination
Hypothesis generation
Types of Descriptive Studies:
Correlational or aggregate studies
Measures the characteristics that represent entire population
Comparison of groups rather than individuals; cannot determine the individual exposure
There is inability to link the exposure with the disease in particular individuals
Ecologic Study (correlational studies) Unit of observation: groups of people Describes disease in relation to a factor of interest Ecological association doesn’t not necessarily translate to an individual level
Types of Descriptive Studies:
Identify what is the:
Exposure: cause (2 Terms: exploratory & etiologic)
Outcome: effect of the exposure
Ecologic unit
Ex: Mortality from lung cancer & per capita cigarette sales
Mortality from liver cancer & per capita alcohol consumption
Ecologic Study
Unit of observation & analysis: group
Represent average exposure and disease levels rather than actual individual levels
Data provided is only for the group
Sources of data: population registries, census, vital registries, large surveys
May use prevalence, incidence or mortality data
Hallmark: use of groups as unit of observation
Exploratory vs Explanatory:
_____: no specific exposure of interest that is measured
_____: the primary exposure variable is measured and also included in the analysis
Exploratory
Etiologic
Types of Ecologic Studies:
subjects are grouped by place
Multi-group design
Constant: time
Varies: place
Ex: The relation between male obesity and income inequality in 21 rich countries (etiologic)
Exposure: income, outcome: % of obesity, ecologic unit: 21 rich countries
Types of Ecologic Studies:
subjects are grouped by time
Time-trend design (ecologic trend)
Constant: place
Varies: time
Ex: Percentage of Children receiving Measles-Mumps-Rubella (MMR) Immunization in Second Year of Life and Caseload of Children With Autism, by Year of Birth, California, 1980- 1994
Exposure: MMR Immunization, outcome: autism, ecologic unit: children in California born in 1980-1994
Types of Ecologic Studies:
subjects are grouped by place and time
Mixed design
No constant
Varies: place and time
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Aims of Ecologic Study
- Generate hypothesis
- Evaluate defectiveness of population interventions
A
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Advantages of Ecologic Study
- High cost and inconvenience
- Overcome measurement limitations of individual-level studies
B
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Advantages of Ecologic Study
- Overcome design limitations of individual-level studies
- No interest in ecological effects
A
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Advantages of Ecologic Study
- Simplicity of analysis and presentation
- Intricacy and complexity of design
A
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Limitations of Ecologic Study
- Cannot link exposure with disease at the individual level
- Lack of ability to control for effects of potential confounding factors
C
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Limitations of Ecologic Study
- Correlational data represent average exposure levels rather than actual individual values
- Individual level relationship of exposure with the disease can be exactly determined.
A
This is what researchers mostly
commits. What they see on the group
level, they associate it on the
individual level.
Ecological fallacy
Methods of Analysis
Graphical: scatter-plot
Computation of: Correlational coefficient (r) and Coefficient of determination
Linear regression analysis: Y = a + bX
Ecologic Study
Types of Descriptive Studies:
Describes the experience of a single patient or group of patients with similar diagnosis
Unit of observation: Individual
Case Report & Case Series
single patient; Document unusual medical occurrences
Represents first clues in the identification of new disease or adverse effects of exposures
New syndromes or variants of known disease; results can formulate hypothesis
Case Report
group of patient; Collection of individual reports
Early means to identify the presence of an epidemic; combining case reports
Investigation of affected individuals can lead to hypothesis generation:
Identification of the disease and identification of specific risk factors
Case Series
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Limitations of Case Report/Case Series
- Can be used to test for the presence of a valid statistical decision
- Not based on experience of a single person/ group of persons only
D
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Limitations of Case Report/Case Series
- Interpretability of information is severely limited by lack of appropriate comparison group
- Has a comparison group
A
Objective: Test a hypothesis
A statement about the relationship between 2 variables (exposure and outcome)
Key Strategy
Use of a comparison group: to estimate the counterfactual scenarios
Controls = Comparison group
Can test hypothesis because of this
Analytical Studies
Types of Analytical Studies:
no assignment and manipulation
Observational
Types of Analytical Studies:
there is manipulation of exposure variable, there is assignment of the exposure variable
Experimental
Exposure (E) and Outcome/ Disease (D) variables are measured at one point in time or over a very short period of time
Difference from Descriptive type: presence of comparison groups
Cross-sectional studies (prevalence studies)
Without comparison groups: descriptive cross-sectional = no controls
Can be analytical or descriptive
One point in time or one time point
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Uses of Cross-sectional studies
- Does not provide information about the frequency and characteristics of the disease by furnishing a “snapshot” of the health experience of the population at a specified time
- Provides information on the prevalence of disease or other health outcomes
B
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Uses of Cross-sectional studies
- Monitor changes in population over time
- Make inference about risk of developing disease
C
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Uses of Cross-sectional studies
- Simply describe the variables
- Determine association between coexisting variables
B
Measures of _____ :
Prevalence proportion
Disease/ prevalence odds
Disease Occurrence
Measures of _____:
Prevalence difference: PD
Prevalence ratio: PR
Odds ratio: OR
Association
PD= PE+ - PE-
0 is the null value
Prevalence Difference
PR= PE+/ PE-
1.0 is the null value
Prevalence Ratio
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Advantages of Cross-sectional studies
- Costly and expensive
- Does not suffer from lost to follow-up: Short-period of time only
B
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Advantages of Cross-sectional studies
- Specific and cannot be generalized
- Generalizable
B
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Limitations of Cross-sectional studies
- Difficult to establish the temporal relationship between study variables
- Unable to establish CAUSALITY; Don’t know if association is causal
C
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Limitations of Cross-sectional studies
- Does not lack information on past exposure
- Never miss disease of short duration or with periods of remission
D
Remission: temporal recovery; disappearance of signs and symptoms
A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct
Limitations of Cross-sectional studies
- Suffer from selection bias
- Free from systematic error
A
survey bias, tendency of a person to answer questions on a survey untruthful or misleadingly
Due to pressure
Response bias
when selection process favors certain individuals who made it past a certain obstacle or point in time and ignores individuals who did not
Survival bias
