... A poorly designed rubric is poison--it can actually lower student performance. ...
The primary problem in poor rubric design comes from a fear of employing subjective judgment. To use technical assessment terms, writers of poor rubrics are so focused on reliability that they ignore validity. If in rubric design you truly focus on validity, you can create a rubric that is both valid and reliable. If instead you focus on reliability, you can create what I call the illusion of objectivity and not realize that your results do not in any way accurately reflect the actual quality of the student's work. You got a nice, clear number, but the number is meaningless.