Abstract: In a computer system for analysis of gene expression data, a gene expression database is organized in a hierarchical b-tree according to the descriptive and clinical sample attributes stored in the database. A user submits a query for searching the database and defines attributes on which to filter for each level of the b-tree. A simple search can be employed to arbitrarily group together leaf nodes depending on their attributes. The grouped leaf nodes are used as “control” and “experimental” sample sets. A t-test can be performed to test for statistically significant regulation between the control and experimental sample sets. In one embodiment, the results of the b-tree analysis are organized as a table of information which may be part of a relational database. The data in the database are encoded according to a three-state scheme based on regulation behavior.