Study Designs Flashcards
Define epidemiology
Study of how often disease occurs in diff grps of ppl + y
What’s another way to say:
-disease occurrence
-risk factors
-disease prognosis
-Disease prevalence
-protective factors
-disease outcomes
Observational studies ?
What investigators do/don’t ?
-question , observe, measure diff factors, record results
-no change or intervention w participants’ lives
Intervention studies?
Investigators do/don’t?
Another name?
-intervention in pre-planned way (e.g. new treatment) - result recorded
Aka experimental studies
3 types of observational studies ?
Cross-sectional
Case-control
Cohort
2 types of intervention ?
-non-randomised
-randomised controlled trial (RCT)
2 things that strength of evidence depend on?
Study design + quality
Define exposure
Risk / protective factor
Cross-sectional study ?
2 types of samples?
2 uses?
Sample from defines pop is surveyed - ‘snapshot’ - all factors (exposure/outcome) measures at one point in time.
-representative or random ?
-asses association between exposure and outcome / asses prevalence of disease
Pros(2) and cons(2) of cross-sectional study ?
-cause and effect relationship hard to determine so not strong evidence
-evidence distorted by confounding factors
-quick
-inexpensive
Cohort study is what? Used to do what?
-group selected - exposure status measures - follow up to see who develops disease outcome
-occurrence in exposed vs unexposed
- assess to association between exposure vs outcome
Cohort studies are 1) longitudinal and 2) prospective … this means what?
1) tracking people over time
2) Following people forward into the future
What are confounding factors?
factors that affect both disease exposure and outcome, and can distort results.
Pros (1) and cons(4) of cohort studies.
- we know exposure comes before disease , so stronger evidence for cause/effect relationship vs cross-sectional
-large numbers needed
-not feasible for very rare diseases
-time consuming + expensive due to large no.s + follow up
-association distorted by confounding factors (same w all observational studies)
What’s a case-control study ? Why is it used ?
How is it carried out?
Which group is ‘case’ or ‘control’
- select group of ppl w/ or w/out outcome disease , then previous exposure status found - compared between 2 groups
-used to find association between exposure and outcome
Case = w disease outcome
Control = w/out disease outcome
Pros(2) and cons (4) of case control study?
-can’t measure risk or prevalence of disease , and we decide no. In each group
- have to use ‘odds’ ration to assess association
-ideal for rare disease
-less expensive and quicker than cohort - smaller no.s and no follow ups
-potential recall error or bias
-association may be distorted w confounding factors
Pros(2) and cons (4) of case control study?
-can’t measure risk or prevalence of disease , and we decide no. In each group
- have to use ‘odds’ ration to assess association
-ideal for rare disease
-less expensive and quicker than cohort - smaller no.s and no follow ups
-potential recall error or bias
-association may be distorted w confounding factors
Does systematic review of observational studies eliminate the issue w confounders?
No
When and how can we deal w confounders
At analysis stage
-use adjusted analysis
-statistical model ( tells us to what extent confounding factors affected results)
What’s an RCT? Used for what ?
-used to find impact of intervention on outcome
-participants recruited - fit criteria - give informed consent
-participants randomised to either intervention or control
-follow up - RCT longitudinal and prospective
-incidence compared in both groups
Disadvantage of RCT ethically
Everyone wants/ needs intervention .
Ensure that everyone eventually get intervention , but control get it after study so it doesn’t affect outcome.
What’s good about randomisation
Ensures similar baseline characteristics of men in both groups
RCT’s have high or low confounders? Why?
Low- due to randomisation
1 pro of RCT and 3 cons
- Strongest evidence for cause and effect relationship
- large number sneezed- time and money consuming
-can’t be used to study exposures that can’t be changed
