BIOSTATISTICS


I. Diagnostic Tests

  Disease Present Disease Absent
Test result is Positive A B
Test result is Negative C D

__A _ = "Sensitivity" aka "True Positive Rate"
A + C

__D _ = "Specificity" aka "True Negative Rate"
B + D

__A _ = "Positive Predictive Value"
A + B

__D _ = "Negative Predictive Value"
C + D

1 - Specificity = "False Positive Rate"

1 - Sensitivity = "False Negative Rate"

True Positive Rate_ = "Positive Likelihood Ratio"
False Positive Rate

False Negative Rate = "Negative Likelihood Ratio"
True Negative Rate

Probability___ = "Odds," often expressed as X:Y
1 - Probability

Odds of an event in one studied group_____ = "Odds Ratio"
Odds of same event in another studied group

"Reliability" = The ability of a test repeatedly to generate the same results given the same conditions

"Validity" = The degree to which a test measures what it is purported to measure

"Bias" = a systematic error that leads to results that do not represent the true findings

"Confounders" = Subject characteristics that are nonrandomly distributed between study groups that affect the results being studied and decrease its validity

II. Effects of Interventions

Events in Control Group - Events in Intervention Group = "Absolute Risk Reduction"

_________1_________ = "Number Needed to Treat"
Absolute Risk Reduction

Risk of disease in one group___ = "Relative Risk"
Risk of disease in another group

 

III. Other terms

"Incidence" = Number of new cases of a disease within a given time period in a given population

"Prevalence" = Number of cases of a disease in a population at a given time

"Kappa value" = A chance-corrected measure of inter-observer agreement. Perfect agreement = kappa of 1.0; absolute disagreement = kappa of 0.  See Landis JR, Koch GG.  The measurement of observer agreement for categorical data.  Biometrics 1977;33:(1):159-74.