1 Flashcards
1
Q
What is an ecological study?
A
- An observational study of a population measuring at least one variable
- Occurrence of disease is compared between groups that have different levels of exposure, thus offering a comparison group for this study
2
Q
What are the advantages of ecological studies?
A
- Quick and cheap
- Can examine patterns by age, sex, ethnicity and/ or time
- Few ethical issues
- Useful for generating a hypothesis
3
Q
What are the disadvantages of an ecological study?
A
- No link between individual exposure and effect
- Bias-variation in diagnostic criteria
- Absence of records of individuals
- Inconsistency in data presentation
4
Q
What is a cross sectional study?
A
- Observational study
- Measures exposure and disease at one point in time
5
Q
What are the advantages of a cross sectional study?
A
- Results generate a hypothesis
- Rapid feedback of current events in community
- Quick and cheap
- Few ethical issues
6
Q
What are the disadvantages of cross sectional studies?
A
- No time reference
- Prone to sampling, subject and observer bias
- Could be just reporting a medial oddity
7
Q
What is a case-control study?
A
- Observational study
- Identifies individuals who develop the disease (cases) and individuals without be disease (controls), then determines both groups previous exposure
8
Q
What are the advantages of case-controlled studies?
A
- Identifying individuals and recruiting controls minimises the number needed for a significant result
- Results can be obtained quickly as disease is already present
9
Q
What are the disadvantages of case-controlled studies?
A
- Retrospective analysis, therefore unreliability in sample recall and incomplete records
- Difficult to say if association is causal
- Prone to selection and information bias
- Incidence cannot be calculated
10
Q
What is a cohort study?
A
- An observational study
- Begins with exposed and non-exposed people who don’t have the disease, study sample is drawn from individuals at risk of developing the outcome
- Individuals are exposed through time until some of them develop the disease; then compare the rate of outcome for both the exposed and non-exposed groups
11
Q
What are the advantages of a cohort study?
A
- Distinguishes between concurrent association factors (suggesting cause and effect)
- Incidence can be calculated; relative and absolute risk
- Study multiple outcomes to one exposure
- Less chance of bias
12
Q
What are the disadvantages of cohort studies?
A
- Cannot be certain exposures are causal without a control group
- Long periods of study and large populations so expensive
- Advancements in Medical science may impact
13
Q
What are controlled studies/ RCTs?
A
- Participants are randomly allocated to investigation treatment or original treatment/ placebo group (control)
14
Q
What are the advantages of RCTs?
A
- Randomisation therefore confounding factors are evenly distributed
- Doctor and patient blind
- Statistical tests for significance are easier when design removes confounders
- Confounders and bias are minimised
15
Q
What are the disadvantages of RCTs?
A
- Large and expensive trials
- Volunteer bias
- Ethical issues in withholding treatment eg control group
