Types of Epidemiological Investigations

Study Notes

Types of Epidemiological Investigations

Descriptive Studies: These studies are conducted without specific hypotheses. They are often the initial investigations into a new disease. The goal is to characterize the disease, quantify its frequency, and determine how it varies based on individual, location, and time. Examples include routine data, case reports, case series, field surveys, and prevalence surveys.
Analytical Studies: These studies analyze observations using statistical and diagnostic tests. The goal is to identify and test hypotheses about the association between an exposure of interest and a particular outcome. Examples include case-control studies, cohort studies, and cross-sectional studies.
Theoretical Studies: This type uses mathematical models to represent disease and simulate patterns of disease occurrence.
Experimental Studies: These analyze data from groups of animals where factors can be altered. Researchers allocate animals into categories and test hypotheses about exposures and outcomes. Importantly, researchers have direct control over the study conditions. Examples include clinical trials, field trials, and community trials.

Descriptive vs. Analytic Epidemiology

Descriptive Epidemiology: Focuses on the "who, what, when, and where" of a disease. It describes the patterns of disease occurrence in a population.
Analytic Epidemiology: Focuses on the "why and how" of a disease. It aims to determine the strength, importance, and statistical significance of epidemiological associations.

Descriptive Epidemiology: Measures

The acronym DMAPT is used in descriptive epidemiology. D = Disease, M = Measures, A = Animals, P = Place, T = Time

Epidemiological Studies: Data Categories

Routine data are collected and submitted by various facilities such as slaughterhouses and laboratories
Case studies/reports are detailed accounts of individual cases
Field surveys are studies of individuals collected in a particular area
Prevalence surveys determine the number of individuals with a specific condition in a specific time period

Additional Considerations

Foot and Mouth Disease (FMD): FMD is a disease with various clinical stages; diagnosis is based on combinations of signs, such as lameness, salivation, smacking of lips, and sores on the mouth, tongue, gums, and lips.
Animal Distribution: Factors considered in animal studies may include species, age, sex, and other relevant variables.
Species affected by FMD in Southeast Asia: Bovines, buffaloes, pigs, and small ruminants are common affected species in Southeast Asia.
Analytic Studies: These studies test hypotheses and focus on the relationships between different factors
Cross-sectional studies: A specific type of analytical study used to measure prevalence. A snapshot of disease distribution in a population; participants are sampled at one point in time.
Case-control studies: A specific type of analytical study used to investigate the association between a factor and the development of a disease. Cases (those with the disease) are compared with controls (those without the disease).
Cohort studies: A specific type of analytical study used to investigate risk factors for a disease. Groups of individuals are followed over time to observe which ones develop the disease.
Experimental Studies: Researchers perform an intervention on a group of animals and assess outcomes
Clinical Trials: A specific type of experimental study conducted to assess the effectiveness of new treatments or prevention measures
Field Trials: A specific type of experimental study involving the application of new treatments or preventive measures under natural field or semi-field conditions
Measures of Risk: Several measures compare risk and determine the association between exposures and disease.
- Relative Risk (RR): Compares the risk of developing the disease between exposed and unexposed groups
- Attributable Risk (AR) / Risk Difference: Measures the additional risk of disease attributable to exposure
- Population Attributable Risk (ARp): The portion of the incidence or risk of disease in a population that can be attributed to the risk factor
- Population Attributable Fraction (AFP): The fraction of cases attributed to the risk factor
Odds Ratio (OR): A measure of association specifically used in case-control studies; it is the odds of exposure among cases relative to the odds of exposure among controls.