Evaluation models either describe what evaluators do or
prescribe what they should do. Generally, evaluators are
concerned with determining the value or current status of
objects or states of affairs.
The term ‘model’ is used in two general ways.
(a) A prescriptive model, the most common type, is a set of
rules, prescriptions, prohibitions, and guiding frameworks
which specify what a good or proper evaluation is and how
evaluation should be carried out. Such models serve as
samples.
(b) A descriptive model is a set of statements and
generalizations which describes, predicts, or explains
evaluation activities. Such models are designed to offer a
practical theory.