The grants in the Federal pain research portfolio were classified using a multi-tiered system. In Tier 1, grants were designated as basic, translational, or clinical. Grants then were coded into 29 scientific topic categories (Tier 2). Following this classification, the Tier 2 categories were organized into 9 overarching themes based on similarity of topic.
http://paindatabase.nih.gov/content/iprp-ontology
