Evidence.statistic.modelCharacteristic currently contains an attributeEstimate element which is recursive (attributeEstimate.attributeEstimate) and a modelCharacteristic element which is recursive (modelCharacteristic.modelCharacteristic).

Modeling complex statistical analysis plans shows that the recursive element structure is necessary but the attributeEstimate structure can meet the need.  It is just not correct to call it an "estimate" in this context.

The proposed changes to Evidence.statistis.modelCharacteristic are:

1. Rename attributeEstimate to attribute 0..* see attributeEstimate
2. Remove modelCharacteristic