Strategies used in Epidemiology

• Research design

  • Enable researcher to logically address research question with minimal ambiguity
  • Play major role in determining scientific value of research study
  • Aid clinicians in practicing evidence-based medicine; guide health promotion activities and help health administrators make informed decisions re allocation of resources
• Descriptive epidemiology

  • Describes population at-risk
  • Collects and analyzes data
  • Addresses who, where, when
  • Sources of data include: census, vital statistics, clinical records
  • Findings lead to formulation of hypothesis
• Analytic epidemiology

  • Tests hypothesis derived from descriptive study
  • Addresses cause and effect (why, how)
  • Identifies and quantifies factors associated with disease or health event
• Descriptive epidemiology


  Concerned with organizing and describing data according to: Person (Who), Place (Where), Time (When)

  
• Types of descriptive studies

  • Case study / case report
  • Case series
  • Cross-sectional
  • Ecological

  
• Case study / case report


  • Detailed report of specific features of a particular case (usually a single individual)
  • Most simple and basic type
  • In conjunction with case series, early detection of emergence of new disease or epidemic may be identified
• Case series


  • Collection of cases studied
  • Include systemic review of the interesting and common features of small group of patients with similar diagnosis
  • In conjunction with case study, early detection of emergence of new disease or epidemic may be identified (provides cues pertaining to cause / course)
• Cross-sectional study


  • Conducted over short period – no follow-up; gives snapshot of the characteristics of participants in a single point of time
  • Persons studied based on being part of a group e.g. diabetics
  • Used to assess prevalence of a disease in a population
• Cross-sectional study

  • Advantages: useful for examining associations among health-related events; can be used to study several associations at once
  • Disadvantages: not useful for rare conditions; cannot generalize to future time points; influenced by response bias; cannot be used to establish cause and effect relationship
• Ecological study


  • Used when data at an individual level is unavailable or, when large-scale comparisons are needed to study population level effect of exposures on a disease condition
  • Type of measures are aggregates of individual level data
  • Generally used in public health research; findings are applicable only at the population level
• Descriptive epidemiology


  • Provides information about new disease
  • Provides clues to identifying new cases
  • Helps to determine extent of public health problem
  • Identifies population at greatest risk
  • Obtains description of problem that can be readily communicated
  • Helps in planning and resource allocation
  • Identifies avenues for research into cause and effect
• Case-control study


  • Focus on outcome to exposure (identified by disease and observed for risk factors / exposure)
  • Two groups of participants: Cases (persons with particular disease or health event) and Controls (persons from general population without disease or health event) who are appropriate match for cases
  • Matching reduces confounding (confounders equally distributed)

  
• Case-control study is a retrospective study – looks in past for possible exposures persons might have had as risk factor
• Odds Ratio (OR)


  • Main outcome measure in case-control studies
  • OR = odds of being exposed (case) ÷ odds of being exposed (control)
  • OR = odds of disease exposed ÷ odds of disease unexposed
• In cohort studies, the numbers of newly occurring (incidence) cases of disease are recorded and compared between groups
• Clinical Trials


  • Used mostly for assessing a new treatment, two types: treatment trial (e.g. drugs, lifestyle modification) and prevention trial (e.g. exercise programme, vaccine)
• RCTs are the most expensive and time-consuming study design, researchers often face issues with the integrity of randomization due to refusals, drops outs, crossovers, and non-compliance, cannot be used if intervention borders on unethical ground
• Non-randomized Controlled Trials


  Do not use random assignment, choice of who receives the intervention is decided in some other way, has the potential to introduce selection bias as group allocation is selected by the researcher
• analytical studies deals with........

  cause and effect