Computerized Adaptive Testing (CAT) A Look into the REx-PN Scoring Method

The REx-PN Uses CAT to Administer the Exam

CAT merges computer technology with modern measurement theory to increase the efficiency of the exam process.

Every time a candidate answers an item, the computer re-estimates their ability based on all the previous answers and the difficulty of those items. The computer then selects the next item that the candidate should have a 50% chance of answering correctly. This way, the next item should not be too easy or too hard. The computer's goal is to get as much information as possible about the candidate’s true ability level. Candidates should find each item challenging as each item is targeted to their ability. With each item answered, the computer's estimate of their ability becomes more precise.

Pass/Fail Rules

The computer decides whether a candidate passed or failed the REx-PN using one of three rules:

  1. 95% Confidence Interval Rule: This scenario is the most common for candidates. The computer will stop administering items when it is 95% certain that the candidate’s ability is either clearly above or clearly below the passing standard.
  2. Maximum-Length Exam Rule: Some candidate’s ability levels will be very close to the passing standard. When this is the case, the computer continues to administer questions until the maximum number of items is reached. At this point, the computer disregards the 95% confidence interval rule and considers only the final ability estimate:
    • If the final ability estimate is above the passing standard, the candidate passes.
    • If the final ability is at or below the passing standard, the candidate fails.
  3. Run-out-of-time (R.O.O.T.) Rule: If the candidate runs out of time before reaching the maximum number of items, the computer has not been able to decide whether the candidate passed or failed with 95% certainty. Therefore, an alternate rule must be used:
    • If the candidate has not answered the minimum number of items, the result will be a failing exam.
    • If the candidate has answered the minimum number of items, then the exam is scored by using the final ability estimate computed from responses to all completed items.
    • If the final ability estimate is above the passing standard, the candidate passes.
    • If the final ability estimate is at or below the passing standard, the candidate fails.