Calling everything statistics was very confusing. Diagnose Targets stratifies the data three ways: Interval, Sample and Locus. Each stratification then has it's own set of metrics (plugin system) to calculate -- LocusMetric, SampleMetric, IntervalMetric.
Metrics are generalized by the Metric interface. (for generic access)
Stratifications are generalized by the AbstractStratification abstract class. (to aggressively limit code duplication)