# USMLE- Epidemiology and biostatistics II

xogamire's version from 2015-04-11 13:28

## Section 1

How can you do an evaluation of a diagnostic test?Use a 2X2 table, you then have true positive (TP), false positive (FP), true negative (TN) and false negative (FN)
What is the definition of sensitivity?Proportion of all people with disease who test positive.
what are the mnemonics for the sensitivity?PID= Positive In Disease and SNOUT= SeNsitivity rules OUT (because 100% of sensitivity is desirable for ruling out disease)
What are the equations for the sensitivity?Sensitivity= TP/ (TP+FN) and Sensitivity= 1- false-negative rate
What is the definition of specificity?Proportion of all people without disease who test negative
What are the mnemonics for the specificity?NIH= Negative In Health and SPIN= SPecificity rules IN
What are the equation for specificity?specificity= TN/(TN+FP) and specificity= 1- false-positive rate
What means positive predictive value (PPV)?proportion of positive test results that are true positive (probability that person actually has the disease given a positive test result)
What is the equation for the PPV?PPV=TP/(TP+FP) and a high pretest probability (high prevalence)=>High PPV
What means negative predictive value (NPV)?proportion of negative test result that are true negative (probability that person actually is disease free given a negative test result)
What is the equation of NPV?NPV= TN/(FN+TN) and a high pretest probability (high prevalence)=>low NPV

## Section 2

What is the mnemonic for incidence?Incidence looks at new incidents
What is the mnemonic for prevalence?prevALence looks at ALL current cases
What is the equation of the incidence rate?incidence rate= (#of new cases in a specified time period)/(population at risk during same period of time)
What is the equation of prevalence?prevalence=(# of existing cases)/(population at risk)