1. A database system, comprising: a plurality of computing hardware nodes for analyzing longitudinal data for a plurality of entities, each computing hardware node comprises at least a memory to store longitudinal data and a processor coupled to the memory, the longitudinal data comprising events of a plurality of types and dates on which the events occurred with respect to the entities, and an index mapping to map events to the entities; wherein at least one or more of the computing hardware nodes to: receive a query definition, access the longitudinal data to identify entities having events that match the query definition, each of the identified matching entities comprising a cohort; generate a transformation measure with respect to each of the identified matching entities in view of the query definition, wherein to generate the transformation measure, the computing hardware nodes further to: identify an event value for the transformation measure associated with at least one entity of the identified matching entities, and apply the transformation measure to related events of the longitudinal data associated with the at least one entity to normalize distribution of the event value with respect to the related events; receive identifiers of the identified matching entities that correspond to the query definition; access the longitudinal data to retrieve events associated with the identifiers and the generated transformation measures for the identified matching entities; and provide results of a statistical analysis performed on the cohort using the longitudinal data.