A structured, well-defined specification for a proposed change.
A related object - the Statistical Need - is a change expression as it has been received by an organization. A Statistical Need is a raw expression of a proposed change, and is not necessarily well-defined. A Change Definition is created when a Statistical Need is analyzed by an organization, and expresses the raw need in well-defined, structured terms.
A Change Definition does not assess the feasibility of the change or propose solutions to deliver the change - this role is satisfied by the Business Case object. The precise structure or organization of a Change Definition can be further specified by rules or standards local to a given organization. It also includes the specific Concepts to be measured and the Population that is under consideration.
Once a Statistical Need has been received, the first step is to do the conceptual work to establish what it is we are trying to measure. The final output of this conceptual work is the Change Definition.
The next step is to assess how we are going to make the measurements - to design a solution and put forward a proposal for a body of work that will deliver on the requirements of the original Statistical Need