Epidemiological Methods: Concepts and Applications
Epidemiological Methods
Epidemiological Methods: The application of scientific method to the field of epidemiology, the phenomena of population health, to understand the causal factors of community health problems.
Limitations
- Variability of phenomena
- Multiple causality of health issues
- Experimentation challenges
- Epidemiological research requires population collaboration
Stages of Epidemiological Research
- Sample epidemiological phenomenon
- Data tabulation and comparison
- Developing a hypothesis (H)
- Experimental testing or verification of H
- Development of a law
Hypothesis (H) Criteria: Not arbitrary, no contradiction with established facts, supported by available data, and no study that demonstrates otherwise.
Descriptive Epidemiology
Observe and discover a phenomenon in terms of three variables: Person, Place, Time.
Analytic Epidemiology
Formulation of a Hypothesis: To issue an opinion based on the reasons for the occurrence of the phenomenon, cause and effect, and risk factors.
Experimentation
Checking or testing of hypotheses in epidemiological studies.
Descriptive Observational Designs
Descriptive studies provide information on health problems and needs, and data on population variables. They do not establish causal relations and do not test hypotheses.
Goals of Descriptive Studies
- Describe the pattern of a disease in a region or community.
- Identify individuals and groups at risk.
- Understand the distribution of epidemiological phenomena in space and time.
- Contribute to the classification of health problems.
- Generate hypotheses.
Delimitation and Quantification of Epidemiological Facts
Characterization of the people affected, where they occur, and when.
Variable People
Age, sex, race, social class, occupation, marital status, religion, family characteristics, hereditary traits.
Variables of Place
Epidemiological place, ecological, administrative or political, rural and urban, international comparisons.
Variable Time
Calendar, chronological, zero, epidemiological, non-periodic variations, annual cycles.
Advantages of Descriptive Studies
Easy, fast, and cheap source of hypotheses.
Disadvantages of Descriptive Studies
Inability to study cause-effect relationships, do not allow predictions.
Case Reports and Case Series
Detection of unknown or not described phenomena in scientific literature, warning signs, no ability to validate hypotheses.
Ecological Studies
Population aggregate data cannot differentiate individuals, used to assess intervention programs.
Disease
Any subjective or objective deviation from a state of well-being; sickness or illness of a population.
Information Sources
- Disease control programs
- Hospital and primary care statistics
- Records of other aid agencies and laboratories
- Morbidity surveys (interviews, health exams)
Types of Diseases
According to Frequency
- Endemic: Consistent prevalence in a population.
- Epidemic: Abnormally high incidence.
As Evolution in Time
- Secular trends
- Changes or cyclical variations
- Seasonal variations
Indicators
Incidence: Number of new cases of a disease occurring in a population during a period of time.
Prevalence: Total number of existing disease cases in a population.
- Period Prevalence: Over a period of time.
- Point Prevalence: At any given time.
Uses of Incidence and Prevalence
Incidence: Causal research, impact of preventive measures.
Prevalence: Planning of health services, estimate of care needs.
Cross-sectional studies: Frequency of chronic diseases.
Longitudinal studies: Frequency of acute progressive diseases (period prevalence and incidence rate).
Causation
Etiological study of the relationship between an exposure, such as taking a medication, and the appearance of a side effect.
Methods
- Inductive: Observation of particular phenomena.
- Deductive: Overall position of special considerations.
Risk Factor
Endogenous or exogenous factor that can be controlled, which precedes the onset of the disease, is associated with an increased likelihood of disease incidence, and has responsibility for its production.
Risk Marker
Restricted to the person variable (uncontrollable endogenous factors that define individuals particularly vulnerable, indicates an increased risk of developing the disease but is not involved in its production).
The Concept of Association
Relationship between two variables significantly greater or less than that due to chance (positive or negative association).
Concept of Independence
To increase or decrease a variable does not follow a similar effect on the other.
Models
Deterministic: If there is C, and only then, E occurs whenever C is present. C is the only cause of E, and E is the only effect of C.
Multicausal: (Chains of epidemiological causal factors).