Term	Definition
Health outcome of interest (HOI)	A health state or condition of an individual, group of people, or population. Examples include hepatic decompensation, rash, or mortality.
Algorithm	Defined set of parameters used to classify the HOI. The simplest algorithm is a single criterion, such as a diagnosis code, to identify the HOI. The algorithm classifies anyone in the study population whose record includes the code during the specified time window as having the condition, and those without the code as not having the condition.
Validation study	Cases identified by the algorithm (or not) are compared with a reference standard and provide estimates on algorithm performance.
Misclassification	A systematic error in the way an individual is assigned to a different category than the one to which they should be assigned. In this context, the incorrect classification of an algorithm with respect to an individual’s HOI due to an error in determination.
Sensitivity	Proportion of true positives correctly identified by the algorithm.
Specificity	Proportion of true negatives correctly identified by the algorithm.
Positive predictive value (PPV)	Proportion of persons identified by the algorithm who are confirmed to have the HOI.
Negative predictive value (NPV)	Proportion of persons not identified by the algorithm who are confirmed not to have the HOI.