question: public final double errorRate ( ) { if ( ! m_ClassIsNominal ) { return Math . sqrt ( m_SumSqrErr / ( m_WithClass - m_Unclassified ) ) ; } if ( m_CostMatrix == null ) { return m_Incorrect / m_WithClass ; } else { return avgCost ( ) ; } }
target:  Returns the estimated error rate or the root mean squared error (if the class is numeric). If a cost matrix was given this error rate gives the average cost.