20. The system of claim 16 in which the assessments include significance measures of the conceptually related variables related to the observed variables.
16. A system, comprising: a programmable processor; a memory storage system in data communication with the programmable processor and storing instructions implementing a machine learning module that cause the programmable processor to perform operations comprising: providing a base model having observed variables and first conceptually related variables related to the observed variables, providing a candidate model having the observed variables and second conceptually related variables related to the observed variables, a comparator for receiving observations assigned to a subset of the observed variables, and for each observation: evaluating the observation by the base model to produce a base assessment of the observation including a subset of the first conceptually related variables, evaluating the observation by the candidate model to produce a second assessment of the observation including a subset of the second conceptually related variables, and determining a similarity measure of the assessment of the observation based on the base assessment and the second assessment, and a sorting module for selecting a subset of observations having similarity scores below a threshold for use in evaluating performance of the candidate model.