Study Designs Flashcards
Descriptive Studies
describe disease:
Characteristics, amount, and distribution of disease
Analytical Studies
Identify associations: Determine if there is an association between an exposure and outcome in a population and how strong the association is
The ultimate goal is to determine if an exposure factor causes the disease
Characteristics of a good study
Scientifically sound
Valid
Precise
Efficient
What are the different types of descriptive study designs?
Case Reports
Case Series
Cross-sectional descriptive studies
What is an analytical experimental study design?
Clinical trials
What is an analytical observational study design that compares groups of populations?
Ecological
What is an analytical observational study design that compares groups of Individuals?
Cross-sectional analytical studies
Case-control
Cohort (prospective and retrospective)
Hypothesis
a statement about an association between an exposure and an outcome
One study subject in a descriptive study design
Case Report
A Few study subjects in a descriptive study design
Case Series
What are the advantages of Case Reports and Case Series?
Require minimal resources
relatively quick to perform
Provide information to stimulate hypotheses and future analytical studies
What are the disadvantages of Case Reports & Case Series?
Small number of cases
Findings may be atypical or aberrant
Strictly descriptive
Findings are not generalizable to the population
A descriptive study design with Lots of study subjects
Cross-sectional study
Cross-sectional study
Sample of the population
Estimate the amount and distribution of disease
Measure of disease occurrence is usually prevalence
What are the steps of a cross-sectional study?
- Select subjects from the source population
- Measure the disease in each study subject
- Calculate the measure of disease occurrence
What are the advantages of a cross-sectional study
Can generalize to the population
Fast and Cheap
Provide good descriptive or baseline for future studies
What are the disadvantages of a cross-sectional study
Not good for causality
Prevalence is of limited value
What are the two types of Analytical studies?
Experimental
Observational
Association
when the exposure if dependent on the outcome
Allocated
Assigned
Blinding
researcher doesn’t know the treatment or exposure status of subjects
Random Selection
Randomly select study subjects for inclusion
Random Allocation
Randomly allocated subjects to exposure groups
What are the advantages of Experimental studies?
Establish causality
Free of bias and confounding
Statistically powerful
Exposures and outcomes are clearly measured during the study - no recall bias
Disadvantages of Experimental studies?
Expensive
Very narrow in scope
Not always ethical to randomly allocate treatment
“Placebo effect”
Loss of follow up can be higher for some treatments
Case control studies
Individual Subjects are selected to represent outcome groups
Subjects are selected because of their outcome status
What are the advantages of Case-control studies?
Short timeline
Can look at multiple risk factors at one time
Good for studying rare diseases
What are the disadvantages of Case-control studies?
Poor selection of controls can invalidate the entire study
Recall bias
Incomplete clinical records
Cohort Studies
Individual subjects are selected to represent exposure groups
What are the two types of Cohort Studies?
Prospective cohort studies
Retrospective Cohort Studies
Prospective cohort study
Forward in time
Retrospective cohort study
Back in time
Subjects are selected based on their exposure status, then their outcome status is determined from their history, by reviewing records, questionnaires, testing them to determine if they have the outcome
Advantages of Prospective cohort studies
Establish Causality
Multiple exposures at one time
study of rare exposures
Disadvantages of Prospective Cohort Studies
Take a long time
deal with changing study populations
Depends upon accurate assessment of exposures and consistent assessment of outcomes over time
Advantages of Retrospective Cohort studies
Short timeline - disease has already occurred
look at multiple exposures at one time
studying rare exposures
Disadvantages of Retrospective Cohort Studies
Not good for establishing causality
Poor selection of controls can invalidate the entire study
Depends upon accurate assessment of diseases that happened in the past
Recall bias
Incomplete clinical records
