The test equating process is designed to calculate differences in the difficulty of examinations among administrations.  In this example common item Rasch-model test equating techniques are used for multiple choice examinations.  By accounting for differences in difficulty across years, all candidates have a comparable opportunity to pass the examination, regardless of when they take the test.  Test equating also insures that the established criterion referenced pass point is maintained across test administrations.  It is expected that different test forms, given for different administrations, will have different levels of difficulty. 

The question is how different in difficulty are the test forms across annual administrations. The data reported are from five different certification examinations that were constructed to meet the established content guidelines of that field.  All of the examinations were analyzed using the Rasch model.  The scaled scores range from 1 to approximately 10.  Higher scaled scores indicate a more difficult test form, while lower scaled scores indicate an easier test form.  The year 1 test difficulty is set at 5.00.  Rasch common item horizontal test equating was used for each of the certification examinations.  The average test difficulty is reported for each of four years, counting the first year.  The last column shows the average change in difficulty during the four year period. 

For these examinations there is some change in test difficulty that needs to be accounted for across years to maintain the criterion referenced standard.  However, for most years, there is not a dramatic change in test difficulty.  Three of the five examinations became more difficult during the four-year period.  However, Exam 5 became easier on average as the years progressed.  For all examinations, except, Exam 1, the changes in the examination were substantial enough to affect the passing and failing candidates if the differences in the difficulty of the test had not been taken into account through the test equating process.