Biostats Flashcards
Cross-Sectional Study
Frequency of disease and frequency of risk-related factors are assessed in the present.
Measures DISEASE PREVALENCE.
Case-Control Study
Compares a group of people with disease to a group without disease.
Measures ODDS RATIO
*Controls and cases are selected based on DISEASE STATUS.
Cohort Study
Compares a group with a given EXPOSURE or RISK FACTOR to a group without such exposure.
Measures RELATIVE RISK
Crossover Study
Compares the effect of a serioes of 2 or more treatments on a participant. Washout period occurs between each treatment.
Allows participants to serve as their own controls.
Twin Concordance Study
Compares the frequency with which both monozygotic twins vs. both dizygotic twins develop the same disease.
Measures HERITABILITY and INFLUENCE OF ENVIRONMENTAL FACTORS
Adoption Study
Compares siblings raised by biological vs. adoptive parents.
Measures HERITABILITY and INFLUENCE OF ENVIRONMENTAL FACTORS.
Clinical Trial - Phase 1
Assesses safety, toxicity, pharmacokinetics, and pharmacodynamics.
Clinical Trial - Phase 2
Assesses treatment efficacy, optimal dosing and adverse effects.
Clinical Trial - Phase 3
Compares the new treatment to the current standard of care
Clinical Trial - Phase 4
Detects rare or long-term adverse effects
Sensitivity
TRUE POSITIVE RATE - portion of all peope with the disease who test positive, or the probability that when the disease is present, the test is positive.
SN-N-OUT: highly sensitive test, when negative, rules OUT disease.
TP/ (TP + FN)
Good for screening tests!
Specificity
TRUE NEGATIVE RATE- Proportion of all people without disease who test negative, or the probability that when the disease is absent, the test is negative
SP-P-IN: high specific test, when positive, rules IN disease.
TN/ (TN + FP)
Positive Predictive Value
Probability that a person who has a positive test result actually has the disease.
PPV= TP / (TP+FP)
Negative Predictive Value
Probability that a person with a negative test result actually does not have the disease.
NPV= TN/(TN+FN)
Lowering Cutoff Value
Increases FP, Decreases FN
Increases sensitivity and NPV
Decreases specificity and PPV
Raising Cutoff Value
Increasing FN, Decreasing FP
Increases specificity and PPV
Decreases sensitivity and NPV
Likelihood Ratios
Likelihood that a given test result would be expected in a patient with the target disorder compared to the liklihood that the same result would be expected in a patient without the target disorder.
LR+= sensitivity/ (1-specificity)= TP rate/FP rate
LR-= (1-sensitivity) / specificity = FN rate/ TN rate
If LR+ >10 and/or LR- <0.1 indicate a very useful diagnostic test
Odds Ratio
Depicts odds of certain outcome given an exposure vs the odds of the outcome in the absence of that exposure
Associate with CASE-CONTROL STUDIES
OR= (a/c)/(b/d) = ad/bc
Relative Risk
Risk of developing disease in the exposed group divided by the risk in the unexposed group.
Associate with COHORT STUDIES (follows people over time)
RR= (a/(a+b))/ (c/(c+d))
RR= 1 : no association b/w exposure and disease
RR>1 : exposure associated with increased disease occurrence
RR<1 : exposure associated with decreased disease occurrence
Relative Risk Reduction
The proportion of risk reduction attributable to the intervention as compared to a control
RRR= 1- RR
Attributable Risk
The difference between exposed and unexposed groups
AR = (a/a+b) - (c/c+d)
AR%
Absolute Risk Reduction
The difference in risk attributable to the intervention as compared to a control
ARR= (c/(c+d)) - (a/(a+b))
Number Needed to Treat
Number of patients who need to be treated for 1 patient to benefit
NNT= 1/ARR
Number Needed to Harm
Numer of patients who need to be exposed to a risk factor for 1 patient to be harmed
NNH= 1/AR
