Sometimes a quantitative measure (referred to as sample trait) is provided for the columns of X. For example, T = (T1, . . ., Tm) could measure survival time or it could be a binary indicator variable (disease status). Abstractly speaking, we define a sample trait T as a vector with m components that correspond to the columns of the data matrix X. A sample trait can be used to define a node significance measure. For example, a trait-based node significance measure can be defined as the absolute value of the correlation between the i-th node profile xi and the sample trait T:
