"The extended scale scores (ESSs) were developed so that progress in reading can be followed over a period of years on a single, continuous scale… ESSs, in effect, rank a student’s achievement within a group that includes all students in all the grades; they relate a student’s achievement to the entire range of achievement during the school years. The ESS scale … measures reading achievement in equal units, so that a difference of, say, 50 ESS units represents the same difference all along the scale.

"Scales of the ESS type are usually developed by choosing a group of students near the middle of the achievement continuum, say, Grade 5 or Grade 6 students, and using the norms for that group as a basis for the entire scale. Several names, such as ‘expanded standard scores’, ‘growth scale,’ ‘universal scale scores’ and ‘developmental scale scores’ are used for scores of this type.

"For the Gates-MacGinitie Reading Tests, there are three ESS scales – one for Vocabulary, one for Comprehension, and one for Total Score. The scales are based on the raw score distributions of the Grade 5 norming group in the Second Edition. Average achievement (Normal Curve Equivalent of 50) at the beginning of Grade 5 (5.1) was represented by an ESS of 500. Average achievement at the beginning of Grade 6 (6.1) by 525. Thus, a difference of 25 ESS units anywhere on the scale represents the difference between the achievement of beginning Grade 5 and beginning Grade 6 students at the time the Second Edition was standardized. To provide continuity from one edition to the next, the same scales have been used for the Third Edition"…. P 18

Manual For Scoring and Interpretation, Third Edition, Level 5/6. Riverside Publishing Company, 8420 Bryn Mawr Avenue, Chicago, IL 60631. (630) 467-7000. [www.riverpub.com]
 
 

The manual for the WRAT3, Wide Range Achievement Test describes it’s Rasch Scale Scores as follows:

"The Rasch analysis provides the opportunity to form an interval scale with the items of the test. This scale is based on the sample of 4,834 persons given the WRAT3 during the standardization period. The Rasch analysis identifies the difficulty level of each item on an interval scale. This original logit scale for each test on each form has been transformed into a scale with a mean of 500….

"The absolute scores of an individual or a group of individuals give measurement of each variable across the whole continuum of that variable without regard to grade or age. These scores allow for a very precise measurement of the academic codes with very little measurement error…. With such scores it is possible to determine where an individual performs on the whole variable scale. Since this data is interval data, comparisons between individuals or within themselves can reliably be made"…. P 33.

Administration Manual. Wide Range, Inc., 15 Ashley Place, Suite 1A, Wilmington, Delaware 19804-1314. (302) 652-4990.