The difficulty index measures the difficulty associated with a given task. The task can be a test associated with an educational course, training program or a work-related task. This is why the index is used by teachers, professionals, trainers and corporate managers. The index is between 0 and 1 and presented in the form of a percentage.
Determine what constitutes a successful result of the exercise or task you are looking to evaluate. As a simple example, assume you are looking to measure the difficulty index of a test administered in a classroom where 70 percent is a passing grade.
Record the number of people participating in the exercise. In our example, assume 20 students will take the test.
Record the number of people who completed the exercise successfully. In our example, assume 13 students pass the test.
Calculate the difficulty index by dividing the number of people who completed the task successfully by the number of people participating in the task. In our example, this is 13/20 which 0.65 or 65 percent. The difficulty index for this example is 65 percent.
The difficulty index can also apply to a specific question, rather than the entire test. You can assess whether a question may be too difficult or too easy by looking at the percentage of students who answered correctly. A test question that doesn't challenge students to think isn't useful in measuring learning, and should be removed.