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26 Cards in this Set
- Front
- Back
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CASE CONTROL study
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Observational & RETRO-spective.
"What happened?" Measured by ODDS RATIO |
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COHORT study
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Observational & PRO-spective.
"What will happen?" Measured by RELATIVE RISK |
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CROSS-SECTIONAL study
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Observational.
"What is happening?" Measured by DISEASE PREVALENCE: shows RF a/w dz but does NOT establish causality. |
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Clinical Trial
Phase ONE |
To Ax:
SAFETY TOXICITY PHARMACOKINETICS |
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Clinical Trial
Phase TWO |
To Ax:
Tx EFFICACY OPTIMAL DOSING ADVERSE EFFECTS |
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Clinical Trial
Phase THREE |
COMPARES new Tx to CURRENT STANDARD of CARE.
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SENSITIVITY
Definition |
Sensitivity
= TP / (TP + FN) = 1 - FN rate Proportion of all ppl WITH dz who test POS. or Ability of a test to detect a dz when it is present. |
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SENSITIVITY
Uses |
Value close to 1 is good for ruling OUT dz (indicates low FN rate). [SNOUT]
Used for SCREENING in dz w/ low prevalence. |
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SPECIFICITY
Definition |
Specificity
= TN / (TN + FP) = 1 - FP rate Proportion of all ppl WITHOUT dz who test NEG. or Ability of a test to indicate no dz when it is absent. |
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SPECIFICITY
Uses |
Value close to 1 is good for ruling IN dz (indicates low FP rate). [SPIN]
Used as a CONFIRMATORY test after a ⊕ screening test. |
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POSITIVE PREDICTIVE VALUE
(PPV) Definition |
PPV = TP / (TP + FP)
Proportion of POS test results that are TP. Probability that person actually has the dz given a ⊕ result. |
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NEGATIVE PREDICTIVE VALUE
(NPV) Definition |
NPV = TN / (FN + TN)
Proportion of NEG test results that are TN. Probability that person actually is dz-free given a ⊝ result. |
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PREVALENCE
Definition |
Point prevalence =
(total cases in popln at a given time) / (total popln at risk at a given time) |
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INCIDENCE
Definition |
Incidence = new incidents =
(NEW cases in popl over a given time period) / (total popln at risk during that time) NB: ppl currently w/ dz or previously ⊕ for it are NOT considered at risk. |
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PREVALENCE
vs INCIDENCE |
Prevalence ≅ Incidence x dz duration
Prevalence > Incidence for CHRONIC dz Prevalence = incidence for ACUTE dz |
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ODDS RATIO (OR)
Definition |
OR
= (a/b) / (c/d) = ad / bc for CASE-CONTROL studies. Odds of having dz in exposed gp vs unexposed gp. |
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RELATIVE RISK (RR)
Definition |
RR
= [a / (a + b)] / [c / (c + d)] for COHORT studies. Relative probability of getting a dz in exposed gp vs unexposed gp. |
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ATTRIBUTABLE RISK
Definition |
AR
= [a / (a + b)] -- [c / (c + d)] Difference in risk btw exposed & unexposed gps or the proportion of dz occurrences that are attributable to the exposure. |
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ABSOLUTE RISK REDUCTION
Definition |
Reduction in risk a/w a Tx as compared to a placebo.
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NUMBER NEEDED TO TREAT (NNT)
Definition |
NNT
= 1 / Absolute risk reduction |
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NUMBER NEEDED to HARM
Definition |
NNH
= 1 / Attributable risk AR = [a / (a + b)] -- [c / (c + d)] |
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BIAS
Ways to REDUCE |
1. BLIND studies (double-blind better)
2. CROSSOVER studies: each subject acts as own control 3. PLACEBO responses 4. RANDOMISATION |
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SELECTION BIAS
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NON-RANDOM assignment to study gp
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RECALL BIAS
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Knowledge of presence of dz alters recall by subjects
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SAMPLING BIAS
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subjects aren't REPRESENTATIVE
relative to general popln so results aren't generalisable. |
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LATE-LOOK BIAS
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info gathered at inappropriate time
e.g. using a survey to study a fatal dz - only pts still alive can answer. |
