EPIB 301 Midterm: Quiz Two Review

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Epidemiology and Biostatistics
EPIB 301

EPIB301 Test 3 Review Ecological vs. Cohort Studies: • Ecological: studies of populations, not individual o Uses things like census data, etc. o Group-level data o Comparison studies & correlation o FALLACY: findings cannot be applied to an individual level ▪ Forces at individual level different than group-level o ADVANTAGES: context of health, can happen when no individualized data, rapid & minimal resources ▪ DISADVANTAGES: fallacy & imprecise measures of exposure • Cohort: population group (with certain characteristic) followed over time: birth, age, work, etc. o Prospective, retrospective & historical perspective cohort studies ▪ Prospective: classified by exposure and observed over time for incidence of disease • Originally no subjects have disease ▪ Retrospective: study is made AFTER some people get disease/outcome, begin identifying/enrolling subjects AFTER outcome occurs • Historical/pre-existing data at baseline used • Not always reliable if based on subject’s memory o ADVANTAGES: direct observation of risk, exposure is well defined, exposures may be uncommon, temporal factor is known o DISADVANTAGES: expensive & time consuming, complicated, subjects may be lost, exposures can be misclassified o Relative Risk used ▪ Incident rate in exposed/incident rate in unexposed ▪ THOSE WHO HAD X had RR TIMES THE RISK COMPARED TO THOSE WHO DID NOT HAVE X o Attributable risk ▪ Difference between incidence rate in exposed vs unexposed • Incidence exposed – incident not exposed ▪ Percent is divided by incidence exposed and multiplied by 100 o Population risk ▪ Incidence in total population – incidence in non-exposed Case Control Studies • Alternative to cohort but much more efficient • Measures association between exposure & outcome • SUBJECTS DEFINED ON BASIS OF PRESENCE OR ABSENCE OF DISEASE OR OUTCOME OF INTEREST o Cases are people with the disease, controls are those who do not have disease • Uses past data from medical records, personal interviews, etc to work backwards and differentiate between cases and controls and differing factors Odds Ratio used in CASE CONTROL • AD/BC o OR > 1 suggests positive association o OR or 2 means association is 2 times higher among exposed o OR < 1 suggests exposure might be a protective factor o OR = 1 suggests no association or not statistically significant • Odds: A/C, B/D Randomized Control Trial • Randomly allocated into study and control groups to receive treatment/prevention • Gold standard Quasi-Experimental Study • Manipulates study factor but does not assign individual subjects randomly to exposed/non exposed groups Threats to Internal Validity of a Study • History o Events occurring with treatment may have impact o Reduced by selecting patients from same location and give same schedule for testing • Maturation o Naturally occurring changes over time may have impact o Reduce by all subjects same age • Testing o Exposure to test can affect scores on later exposures to that same test, may have impact o Different tests to yield different variables o Less threat when time between pre and post-test is large • Instrumentation o Changes in equipment (calibration, adjustment, etc) can have impact o
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