What are the 3 components of epidemiology?
1. Measure disease frequency – Quantify disease 2. Assess distribution of disease – Who is getting disease? – Where is disease occurring? – When is disease occurring? --->Formulation of hypotheses concerning causal and preventive factors 3. Identify determinants of disease
What are the 2 types of primary studies?
- Descriptive studies (describe occurrence of outcome)
- Analytic studies (describe association between
exposure and outcome)
What is the big picture reason for an epidemiological study?
To prevent and control disease
What are the types (designs) of descriptive studies?
- case report
- case series
- descriptive epidemiology
What are the types (designs) of analytic studies?
Observational Studies 1. ecologic study 2. cross-sectional study 3. case-control study 4. case-crossover study 5. cohort study Experimental Studies 6. RCT (randomized controlled trials) 7. community trials
What is a prospective study?
looks forward, looks to the future, examines future
events, follows a condition, concern or disease into the future
What is a retrospective study?
looks back in time to study events that have already occurred
What are case reports?
Detailed presentation of a single case or handful of cases. Generally report a new or unique finding • e.g. previous undescribed disease • e.g. unexpected link between diseases • e.g. unexpected new therapeutic effect • e.g. adverse events
What is a case series?
analysis of the experience of a group of patients with a similar diagnosis
What are the advantages of a case series?
- Useful for hypothesis generation
- Informative for very rare disease with few established risk factors
- Characterizes averages for disorder
What are the disadvantages of a case series?
- Cannot study cause and effect relationships
* Cannot assess disease frequency
What are cross-sectional studies?
exposures and disease status at a single point in time (a cross-section of the population)
What are cross-sectional studies good for?
to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions)
Do cross-sectional studies measure incidence or prevalence of disease?
prevalence
What are cross-sectional studies not useful for studying?
rare or highly fatal diseases or a disease with short duration of expression
What are the disadvantages of cross-sectional studies?
- Weakest observational design
- The temporal sequence of exposure and effect may be difficult or impossible to determine
- Usually don’t know when disease occurred
- Rare events and quickly emerging diseases a problem.
What are case control studies?
an “observational” design comparing exposures in disease cases vs. healthy controls from same population; exposure data collected retrospectively
What kind of study is best for when disease
outcomes are rare?
case control study
What are the advantages of case control studies?
– Less expensive and time consuming
– Efficient for studying rare diseases
What are the limitations of case control studies?
– Inappropriate when disease outcome for a specific
exposure is not known at start of study
– Exposure measurements taken after disease
occurrence
– Disease status can influence selection of subjects
What are the strengths of a cohort study?
– Exposure status determined before disease detection
– Subjects selected before disease detection
– Can study several outcomes for each exposure
What are the limitations of a cohort study?
– Expensive and time-consuming
– Inefficient for rare diseases or diseases with long latency
– Loss to follow-up
What is a cohort study?
an “observational” design comparing individuals with a known risk factor or exposure with others without the risk factor or exposure; looking for a difference in the risk (incidence) of a disease over time
What is the best observational design?
cohort study
