Woodcock Johnson III Diagnostic Reading Battery
Interpretive Information

Contents of this module are from Mather & Jaffe (2002) and Schrank, Mather, & Woodcock (2004)

Available Scores on the WJIII DRB

Raw Scores

(number correct, number of points, or number of errors)

Age or Grade Equivalents

(reflects age or grade level at which average score is same as subject's raw score)

Relative Proficiency Index (RPI)

(RPI=0/90 to 100/90)

Standard Scores, Percentile Rank

(Mean=100, SD=15)

Range: SS= 0-200+, PR=0.1 to 99.9

T scores, z scores, NCEs, Stanines, or CALP scores

Discrepancy Scores (SD, PR)

Age or Grade Equivalents

Age and grade equivalents reflect the age or grade level at which average score is same as subject's raw score.

A grade or age quivalent is another way to compare a student to the standardization sample. If a student receives a grade equivalent of 2.0, it means the student scored the same as the mean (average) raw score of all the second grade students in the standardization sample. For example, if a student's raw score is 25 and the mean raw score for second-grade students in the standardization sample is 25, then the grade equivalent is 2.0. Age equivalents work the same way, except the score represents a comparison to the individuals in the standardization sample that are the same age (Mercer & Pullen, 2009, p. 92).

Relative Proficiency Index

The Relataive Proficiency Index (RPI) predicts a student's level of proficiency on tasks that typical age- or grade-peers would perform with 90% proficiency. For example, an RPI of 55/90 on the Letter-Word Identification subtest would indicate that on similar tasks, the student would demonstrate 55% profiencieny, whereas age- or grade-peers would demonstrate 90% accuracy.

The RPI can document a performance deficit that may not be apparent based on the peer comparison (standard score, percentile rank).

Interpretation Guidelines

The RPI score may be compared to a score on an Informal Reading Inventory for interpretive purposes. Paralleling IRI criteria are as follows:

Independent Level = RPI 96/90 or above (EASY)

Instructional Level = RPI 76/90 to 95/90http://www.ascd.org/ASCD/images/publications/books/marzano2001a_fig1.1.gif

Frustration Level = RPI 75/90 or below (DIFFICULT)

Criterion Referenced Interpretation of RPI Scores

Mather & Jaffe, 2002

Example of the Interpretation of the RPI

Tommy, a second grade boy, obtained a Standard Score of 92 and a Percentile Rank of 30 on the Letter-Word Identification test. His RPI score was a 62/90. These scores suggest that, even though many other second-graders (30%) demonstrated equally limited or more limited sight vocabularies, Tommy's skills were nonetheless deficient compared to the average proficiency of second graders. He requires additional attention in sight word acquisition.

Understanding Standard Scores

The major purpose of standard scores is to place scores for any individual on any variable having any mean and standard deviation on the same standard scale so that comparisons can be made. Without some standard scale, comparisons across individuals and/or across variables would be difficult to make (Lomax,2001, p. 68). In other words, a standard score is another way to comapre a student's performance to that of the standardization sample. A standard score (or scaled score) is calculated by taking the raw score and transforming it to a common scale. A standard score is based on a normal distrbution with a mean and a standard deviation (see Figure 1). The black line at the center of the distribution represents the mean. The turquoise lines represent standard deviations.

Figure 1.

On many standardized assessments the publishers base the standard score on a distribution with a mean of 100 and a standard deviation of 15. A score of 100 on such a test (e.g., WJIIIDRB) means that if the student scored in the middle of the distribution (Mercer & Pullen, 2009). A Standard Score of 85 indicates that the student scored one standard deviation below the mean of the normative sample. Figure 2 illustrates a normal distribution of test scores with a mean of 100 and a standard deviation of 15. The standard deviation is an indication of the variability of scores in a population (Mather & Jaffe, 2002).

Figure 2.

Percentile Ranks

Percentile ranks describe a student's relative standing in a comparison group on a scale of 1 to 99. The student's percentile rank indicates the percentage of students from the comparison group who had scores the same of lower than the student's score. A student's percentile rank of 68 indicates that 68% of the comparison group had scores the same or lower than the student's score. The table below provides the classification of standard scores and percentile ranks of the WJIII DRB.