Clinical Epidemiology Flashcards
Clinical Epidemiology
The study of the patterns, causes and effects of health and disease in patient populations and the relationships between exposures or treatments and health outcomes.
(bioscience= animals models, genes/cells.
clinical sciences= patients
epidemiology= populations
health services research= heath care systems)
What does clinical epidemiology do?
Seeks to answer clinical questions and to guide clinical decision making.
Uses epidemiological approaches applied to groups of individuals seen by health care providers.
Provides the foundation for evidence-based medicine.
What are its clinical applications?
- research question
-study population
-exposure
-outcome
-bias/confounding
-risk estimation
-impact
Types of research questions
Risk:
What factors are associated with increased risk of disease?
Screening/prevention:
What interventions prevent people getting a disease?
Will early detection change the course of the disease?
Prognosis:
What is the natural history of the disease?
What factors determine disease outcomes?
Treatment:
Which treatment is more effective?
What are the unintended consequences of treatment?
How are study population groups defined?
Specific illness or disease
Symptoms/ disease characteristics
At risk population
Diagnostic procedure
Treatment
Clinical epi exposures
interventions (i.e prevention, screening)
patient characteristics (i.e age, ethnicity, clinical features)
treatments or procedures (i.e type, intensity, dose)
Outcome in clinical epi
mortality (i.e survival)
disease progression (i.e recurrence)
morbidity/ complications
Outcomes are usually more frequent in clinical epidemiology compared with population studies
Data sources in clinical epi
Patient registries
Electronic health records
Population health surveys
Routinely collected administrative data
Primary patient-level data collection (prospective or retrospective)
Data collection can be:
study specific (protocol driven)
routine (practice driven i.e hospital records)
combination (i.e clinical registry or patient cohort)
Bias in clinical studies
Selection bias
- study population differs from broader population who would receive intervention in terms of relationship between exposure and outcome (i.e self-selection of participants)
Information bias (measurement error, mis-classification)
- methods of measurement of outcome differ between groups (closer monitoring of one treatment group)
Confounding:
- factors associated with both exposure and outcome may distort the main effect if not taken into account.
Methods to control for bias
Randomisation: selection bias/confounding
Restricted sample: selection bias/confounding
Blinding: measurement bias
Matching: selection bias/ confounding
Stratification: selection bias/ confounding
Multivariate analysis: confounding
Sensitivity analyses: all potential biases
Validity of clinical epi study findings
Internal validity
- Are the findings of the study correct?
- Depends on study design and appropriate analysis
External validity
- Are the findings generalisable to the broader population?
- Depends on study sample & setting
Types of clinical epi study designs:
Observational (non-randomised) studies
- Case-control studies
- Cohort studies
- Ecological studies (aggregated population data)
- Cross-sectional
Randomised studies
- RCTs –> Gold standard (but not always feasible)
Meta-analyses
- Combining results of multiple similar studies
Levels of clinical epi evidence
Meta-analysis RCTs
- All evidence from trials
- Combines data from multiple trials
Level: high
Randomised controlled trials (RCTs)
- Least biased: comparison groups should be equivalent (in all other ways) die to randomised assignment
Level: high
Meta-analyses of observational studies
- Combines data from multiple studies of same type
- Increases statistical power
Level: medium
Observational studies
(Cohort & Case-control)
- Data at the individual level on exposures and outcomes
- Biased if comparison groups differ in underlying risks that affect outcome
Level: medium
Observational studies (Ecological/trend analyses/cross-sectional)
- Data are at an aggregate level so findings may not translate to individuals
- Indicative rather than definitive
Level: low
RCTS
Patients are randomly assigned to one of two or more groups being offered different therapeutic measures
Chance alone indicated whether a particular patient will be assigned to a particular group
Patient outcomes in each group are monitored
- The occurrence of event(s) that the intervention seeks to prevent, and/or
-The occurrence of side effects/adverse effects
Non-randomised (observational studies)
Treatment not assigned as part of study protocol but rather occurs as part of clinical practice
Observe outcomes (prospective or retrospective) following treatment
Observed alternative therapies may be the result of underlying differences between the groups that affect the chance of progression or complications (Bias)
