Types of Epidemiological Investigations

Types of Epidemiological Investigations

• Descriptive: Studies conducted without a specific hypothesis. These are often the initial studies on a new disease. They characterize the disease, quantify its frequency, and determine how it varies based on individual, location, and time.
• Analytical: 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.
• Theoretical: These studies use mathematical models of disease to simulate natural patterns of disease occurrence.
• Experimental: These studies analyze data from animal groups, in which the investigator can alter factors associated with the groups. Researchers can allocate animals to categories and test hypotheses about exposures and outcomes. The key difference is that experimental studies give the researcher direct control over study conditions.

Examples of Epidemiological Investigations

• Descriptive: Routine data, case reports, case series, field surveys, and prevalence surveys.
• Analytical: Case-control studies, cohort studies, and cross-sectional studies.
• Theoretical: Mathematical modeling and prediction studies.
• Experimental: Clinical trials, field trials, and community trials.

Descriptive vs. Analytical Epidemiology

• Descriptive Epidemiology: Focuses on the "who, what, when, and where" of a disease.
• Analytical Epidemiology: Focuses on the "why and how" of a disease.

Descriptive Epidemiology - DMAPT Time

• D: Disease
• M: Measures
• A: Animals
• P: Place
• T: Time

Measures of Disease Frequency

• Morbidity:
  • Prevalence: Proportion of a population affected by a disease at a specific time.
  • Incidence: Rate of new cases of a disease in a population over a specific time period.
  • Attack rate: Proportion of individuals exposed to a disease that develop the disease over a specific time period.
• Mortality:
  • Crude mortality rate: Number of deaths in a population over a specific time period.
  • Case fatality rate: Proportion of individuals with a disease who die from that disease.

Animal Distribution

• Key considerations when evaluating disease distribution: Species/type, age, sex, and other relevant characteristics.

Foot and Mouth Disease (FMD)

• FMD is suspected when animals show a combination of certain symptoms, such as lameness, salivation, mouth lesions, and reduced milk production in lactating animals.

Case Report

• A detailed account of a single case of a disease.

Case Series

• A collection of case reports.

Field Survey

• Locally known as a KAP survey, gathering information on knowledge, attitudes, and practices.

Prevalence Survey

• A cross-sectional survey that rapidly samples a population to determine disease status and exposure status simultaneously.

Analytical Studies - Comparison

• Cross-sectional: A snapshot in time, assessing prevalence but not incidence.
• Cohort: Prospective or retrospective, assessing incidence.
• Case-control: Retrospective, assessing odds ratios.

Epidemiological Studies - Hierarchy of Evidence

• A pyramid-shaped diagram shows the hierarchy of evidence, with randomized controlled trials at the top and case series at the bottom.

Risk Factors

• Risk: The probability of an unfavorable event.
• Risk factors: Factors associated with an increased risk of developing a disease or dying.
• Risk assessments: Analyzing factors that influence risk evaluations (factors such as long latency periods, high prevalence of risk/disease factors, low incidence/disease frequency, and multiple causes of disease).

Measure of Association – Relative Risk

• Common in cohort studies, it's the ratio of incidence in the exposed group to the incidence in the non-exposed group (IE / le).
• If RR = 1.0, there's no difference in risk between exposed and non-exposed groups.
• RR > 1.0 signifies an elevated risk in the exposed group, while RR < 1.0 indicates a lowered risk.
  • Larger RR values correspond to stronger associations.

Attributable Risk (Risk Difference)

• Represents the additional incidence of disease attributable to a risk/exposure factor. Calculated as: IE - le.
• Indicates the difference in disease incidence between exposed and non-exposed groups.

Population Attributable Risk (PAR)

• Estimates the proportion of disease in a population that could be prevented by eliminating a specific risk factor. Calculated as: ARP = AR * P.
• Shows how much a risk factor contributes to the overall disease incidence in a population considering the overall prevalence of the risk factor.

Population Attributable Fraction (PAF)

• Indicates the proportion of disease in a population attributable to a specific risk factor. Calculated as: AFP = ARP / total incidence.
• useful measure of the magnitude of the impact of a specific risk factor.

Experimental Studies or Interventions Studies

• Research studies where an intervention (treatment or preventive measure) is intentionally introduced to assess its effectiveness.
• Often involve clinical trials and field trials.
• Clinical trials are usually conducted in controlled laboratory or clinic settings, while field trials use natural settings.

Clinical Trials

• Experiments where new treatments or preventive measures (like vaccines) are tried on human or animal subjects.
• Aimed at evaluating the effectiveness of a treatment.

Field Trials

• Comparative studies of new treatments or preventive measures.
• Applied in natural or semi-natural settings, like farmlands or field conditions to observe the effectiveness.

Odds Ratio

• Commonly calculated in case-control studies, it's the ratio of odds of exposure among cases to odds of exposure among controls.
• OR = (a/c) / (b/d) = ad/bc.
• Indicates the strength of an association between exposure and outcome. OR > 1.0 indicates a positive association. OR < 1.0 means negative association. OR = 1.0, no association.

Explore the various types of epidemiological investigations, including descriptive, analytical, theoretical, and experimental studies. This quiz delves into how each type contributes to our understanding of diseases. Test your knowledge on the definitions and applications of these crucial research methodologies.