Types of Criteria
If you are evaluating a concrete canoe for an engineering class, you will use concrete criteria such as float time, cost of materials, hydrodynamic design, and so on. If you are evaluating the suitability of a textbook for a history class, you will probably rely on more abstract criteria such as readability, length, and controversial vs. mainstream interpretation of history.
In evaluation, we often rely on concrete, measurable standards according to which subjects (usually objects) may be evaluated. For example, cars may be evaluated according to the criteria of size, speed, or cost.
Many academic evaluations, however, don't focus on objects that we can measure in terms of size, speed, or cost. Rather, they look at somewhat more abstract concepts (problems and solutions often), which we might measure in terms of "effectiveness," "feasibility," or other abstract criteria. When writing this kind of evaluation, it is vital to be as clear as possible when articulating, defining, and using your criteria, since not all readers are likely to understand and agree with these criteria as readily as they would understand and agree with concrete criteria.