Using Clear and Well-defined Criteria
When we evaluate informally (passing judgments during the course of conversation, for instance), we typically assume that our criteria are self-evident and require no explanation. However, in written evaluation, it is often necessary that we clarify and define our criteria in order to make a persuasive evaluative argument.
Criteria That Are Too Vague or Personal
Although we frequently find ourselves needing to use abstract criteria like "feasibility" or "effectiveness," we also must avoid using criteria that are overly vague or personal and difficult to support with evidence. As evaluators, we must steer clear of criteria that are matters of taste, belief, or personal preference. For example, the "best" lamp might simply be the one that you think looks prettiest in your home. If you depend on a criterion like "pretty in my home," and neglect to use more common, shared criteria like "brightness," "cost," and "weight," you are probably relying on a criterion that is too specific to your own personal preferences. To make "pretty in my home" an effective criterion, you would need to explain what "pretty in my home" means and how it might relate to other people's value systems. (For example: "Lamp A is attractive because it is an unoffensive style and color that would be appropriate for many people's decorating tastes.")
Using Criteria Based on the Appropriate "Class" of Subjects
When you make judgments, it is important that you use criteria that are appropriate to the type of object, person, policy, etc. that you are examining. If you are evaluating Steven Spielburg's film, Schindler's List, for instance, it is unfair to criticize it because it isn't a knee-slapper. Because "Schindler's List" is a drama and not a comedy, using the criterion of "humor" is inappropriate.
Once you have established criteria for your evaluation of a subject, it is necessary to decide which of these criteria are most important. For example, if you are evaluating a Mexican restaurant and you have arrived at several criteria (variety of items on the menu, spiciness of the food, size of the portions, decor, and service), you need to decide which of these criteria are most critical to your evaluation. If the size of the portions is good, but the service is bad, can you give the restaurant a good rating? What about if the decor is attractive, but the food is bland? Once you have placed your criteria in a hierarchy of importance, it is much easier to make decisions like these.