Ill. Admin. Code tit. 23 , 25 app A
The Z-score formula set forth below will be used in all cases except where none of the scorable items on a test form has appeared on any previous test form. In such cases, the linear equating formula will be used.
Z-Score Formula
The following formula is used for z-score equating.
1. Define:
2. Set zx = zy
3. In order to find the equivalent passing score on the new form, solve for Xi, where Yi = the passing score on the previous form rounded to one decimal place.
The linear equating formula is as follows.
1. Define:
2. Compute estimated descriptive statistics for the total group (i.e., candidates from new and previous test form administrations).
3. In order to find the equivalent passing score on the new form, solve for Xi, where Yi = the passing score on the previous form rounded to one decimal place.
Ill. Admin. Code tit. 23 , 25 app A