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10 Cards in this Set

  • Front
  • Back
the occurrence of an outcome increases/decreases with the level of exposure

* if associated, the relationship may/not be causal
Ecological Study
* use average group data to assess exposure and outcome in POPULATIONS

* Advantages:
- grouped data may reflect best exposure
- easier to detect exposure differences btw groups than within
- useful in identifying problems
- inexpensive b/c data already collected

* disadvantages:
- ecological fallacy: ppl with outcome may not be the ones w/ exposure
- groups usually differ in other ways beside exposure
- group data may vary in quality
- possible selection bias
Observational Study
describes relationship between exposure and outcome in pop'n at a single point in time

1) begin with defined study group
2) measure exposure and outcome simultaneously
3) classify and compare groups

* advantages:
- useful to describe healthy pop'ns
- associations found can be useful in hypothesizing
- efficient and quick

* disadvantages:
- can't determine cause and effect btw exposure & outcome
- can't sort out existing (prevalent) outcomes from new (incident) outcomes
- can have problems in selecting subjects & making measurements
Case Control Study
1) start with diseased cases (outcome)
- select controls
- controls can be matched/unmatched
2) go back in time to determine exposure in both groups
3) classify by exposure
4) compare exposure rates from cases and contols

* most case control studies use incident cases to describe factors associated with disease development

* advantages:
- efficient, cheap, quick
- only feasible method for rare outcomes
- can evaluate wide ranges of exposures

* disadvantages:
- difficult to select cases and controls
- retrospectively asseses exposure
- not able to assess cause-effect relationship
- can't tell you about development of disease
Prospective Cohort Study
describes the relationship between exposure and development of outcom over time

* advantages:
- study disease development over time
- investigator can control methods of data collection
- allows exposure to occur before disease
- provides best evidence for a cause-effect relationship

* diadvantages:
- can take a long time for results
- expensive
- not good for rare outcomes
Prospective Cohort Study
1) identify study group based on existing records
- data on exposure and outcomes were prospectively recorded in the past
2) classify exposure based on records
3) analyze subsequent outcome from records

* advantages:
- studies outcome development over time
- less bias in assessing exposure
- best observational design for cause-effect

* disadvantages:
- time consuming
- expensive
- need large numbers
- exposures can change over time
- no response, loss to follow-up, surveillance bias
Retrospetive Cohort Study
1) identify study group using existing records where data on exposure and outcome were prospectively recorded in the past
2) classify exposure based on records
3) analyze subsequent outcome from records

* advantages:
- because data already collected, less expensive, quicker
- other advantages of cohort study

* disadvantages:
- record data may not be of uniform quality/available
Nested Case Control Study
1) identify the cases and controls from a cohort where data on exposure and outcome were prospectively collected

2) classify exposure of the cases and controls based on the already-collectd cohort data

* case control study is nested within a cohort

* advantages:
- quick, less expensive, good for rare outomes
- exposure data collected and recorded before outcome occurred
- know underlying pop'n: cases & ctrls may be more representative
- depends on recorded/stored data
Variations of Cohort Study
1) prospective: enroll in present, follow in future

2) retrospective: same direction, but all data already collected for another purpose

3) nested case control: case control study performed using data collected for a prospective cohort study
Randomized Control Trials
* tests how well an intervention prevents an outcome

* exposure (treatment) is assigned by investigtors & applied to INDIVIDUALS

1) select study group
2) divide study group into treatment and control
3) apply intervention
4) assess and compare outcome in treated and control groups

* advantages:
- strongset evidence for causality
- if randomized, selection bias and confounding removed
- if blinded, less observer bias
- meta analysis: can pool results of several studies

* disadvantages:
- not real life
- high cost
- inappropriate/unethical for many investigations
- can have poor compliance, loss to follow-up