Step 5. Stopping rules
In CAT, the composition of the test is adapted to the performance of the candidate. Because of this, high and low performing candidates will answer different sets of items, and measurement precision might vary over candidates. To compensate, a CAT could be terminated when a pre-defined level of measurement precision is reached. In this way it is guaranteed that all candidates are measured with the same level of precision, even though some candidates might have to answer more questions than others. For some applications a variable length CAT might not be feasible, either because the content of the test is specified into detail, or because candidates might perceive a variable test length as unfair. For these applications, a CAT could be terminated after a fixed number of items. A third stopping rule, sometimes combined with either variable length or fixed length CAT, is to set a time limit for the whole test. For practical reasons this is very convenient, but one should be aware of the risks of making the test speeded, which might threat test validity.