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HLW
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What is the main objective of randomized clinical trials?
test the possible effect of a therapeutic or preventive intervention
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What is the main difference between randomized clinical trials and experimental studies?
in experimental studies the investigator has direct control over study conditions
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How is bias avoided in RCT?
- animals randomly allocated to treatment and control groups
- less opportunity for error since not controlled by investigator
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What trials evaluate efficacy of therapeutic agent or novel procedure?
therapeutic trial
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What evaluates whether agent or procedure reduces risk of disease developing in those currently free of disease? (ie. vaccination study)
prevention/field trial
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What is the difference between open and blinded study? Double blinded?
- open: subject and investigator know which are assigned to tx
- blinded: investigator know but subjects are unaware of tx
- double-blinded: both subject and investigator are unaware
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What are strengths of clinical trial?
- researcher has control over study situation (not observational)
- best measure for causal relationship
- randomization minimizes confounding /removes selection bias
- blinding eliminates selection and observation bias
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What are weaknesses of clinical trial?
- excessive control of study means it does not accurately represent real situation
- large sample size needed/costly
- long duration is new case occurrence is low
- ethical considerations
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What type of testing is done to apparently healthy members to detect presence of disease?
screening test
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what type of testing confirms or classifies disease status, guides treatment and provides prognosis?
diagnostic test
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Why are false positives a problem?
waste of money; subjected to more sophisticated testing
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Why are false negatives a problem?
- misdiagnosed during early stages when possibly still treatable
- and allows infected individual to be source for others
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What are 2 components of validity?
sensitivity and specificity
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What is defined as proportion of subjects with disease that test positive (true positives)?
sensitivity
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What is defined as proportion subjects without disease that test negative (true negatives)?
specificity
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What is required to evaluate sensitivity and specificity of new test?
use gold standard test to evaluate before apply new test
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Does the test have high sensitivity or specificity if you trust negative results, thus use the test to rule disease OUT?
- hi sensitivity
- (SNOUT and spin = sensitivity rules dz OUT)
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Does the test have high sensitivity or specificity if you trust positive results, thus use test to rule disease IN?
- hi specificity
- (snout and SPIN = specificity rules dz IN)
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What type of variable requires an established cut off point to determine if results are +/- ?
continuous variable (ie. glucose, blood pressure)
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What type of variable gives a simple positive or negative result?
dichotomous variable/results
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How do you calculate sensitivity?
true positives / total disease positives
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When using the table, do you use columns or rows to evaluate sensitivity/specificity? What about for predictive value?
- columns for sens/spec
- rows for pred.value
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How do you calculate specificity?
true negatives / total disease negative
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What is positive predictive value? How do you calculate positive PV?
- proportion of subjects with POSITIVE test results that HAVE the disease
- true positive / test positive
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What is a negative predictive value? How do you calculate it?
- proportion of subjects with NEGATIVE test results which do NOT have disease
- true negative / test negative
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