Topic 17: observational studies Flashcards
(11 cards)
Give the 2 types of observational study designs
1) Case control
2) Cohort
- Prospective
- Retrospective
Give the types of descriptive study designs
1) Cross-sectional
Describe cross-sectional study
- Mainstay of descriptive epidemiology
- AKA prevalence studies
- Select sample of individual subjects + report rates
- Observe time trends
- Survey population of interest
- Measurements usually present but can be with past exposures
- E.g. rate of disease in children in a country in a specifc year
Give the advatages/disadvantages of cross-sectional study
ADVANTAGES:
- Easy to perform
- Less costly
- Many outcomes can be assessed simultaneously
- Readily assess prevalence of disease + association
- Useful to generate hypothesis
- No loss to follow-up
DISADVANTAGES:
- Information bias = self reports
- Confounding
- Impossible to assess risk = no follow up
- Impossible to establish temporality in association
Describe case-control studies
- Group of patients with specific disease recruited = case group
- Group of random sample not suffering disease = control
- Suitable for = rare conditions + past = retrospective = identify exposure
- Case + control group matched for key characteristics = eliminate confounding
Give the advantages/disadvantages of case-control study
ADVANTAGES:
- Able to investigate determinants of rare diseases
- Easy to perform + cheap
- Assess several exposures for single outcome
- Investigate exposures from early life relating to outcome
DISADVANTAGES:
- Selection bias
- Information bias = self-reports
- Confounding
- Impossible to asess risk of disease
- Can’t establish temporality in association
Describe cohort studies
- Looks at effects of exposure on outcome
- Determine association between exposure + outcome = whether exposure effects liklihood of getting didease
-Subjects = disease free but risk of outcome - Subjects split = exposed/unexposed
1) Prospective = follow up
2) Retrospective = determine exposure based on history
Describe the selection for cohort study participants
- Random sampling = 2 groups on exposure
- Participants suffering = excluded
- Prevalence of outcome at start should = 0
- Initiation = all exposured assessed + potential confounders
- Participants live life normally
Give the advantages of cohort study
- Best method to determine new cases + natural history of disease
- Can investigate multiple outcomes + exposures
- Investigate rare exposures
- Longitudinal measurements = insight of changes over time + dose-response relationship
Give the limitations of cohort studies
- Costly
- Prone to drop out = loss to follow up
- Long time
- Require accurate record for retrospective
- Not best for rare outcome study = large sample size required
Give the advantages/disadvantages of cohort studies
ADVANTAGES:
- Assess risk of disease + mortality
- Assess temporal association
- Assess several exposures + outcomes
- Investigate risk factors for chronic diseases that take years to develop
- Large study sample = increase validity
DISADVANTAGE:
- Information bias = self-reports
- Confounding
- Selection bias = if selevtive drop out
- Hard to investigate rare diseases/with long latency period = very large sample + time needed
- Difficult to conduct = high cost + time
