OWLS-II: Development of Standard Scores per Scale

The original Oral and Written Language Scales (OWLS) were developed to measure language and used widely as a valid assessment by a range of professions. Revisions to the OWLS improved on a number of factors and became the basis for the OWLS-II assessment. It preserves the comprehensive features of the OWLS and develops new enhancements.

Revised scoring software, a new reading comprehension test, and updated artwork are part of these enhancements. Experts evaluated the assessment, examined user feedback, and performed tryouts to ensure both the reliability and accuracy of the improvements.

Standardizing the scores for each scale ensures that they are accurate and they enable a consistent evaluation of individuals being examined. The process for developing these standard scores was intended to identify the best way to score each scale.

Derivation of Standard Scores

Because children develop much more quickly at younger ages, the norms for the OWLS-II were created in three-month intervals for ages three to seven, six-month intervals for ages eight to twelve, and one-year intervals for ages thirteen to fifteen, while a combination of age years was used for ages sixteen to twenty-one.

A Quick Word about Composite Scores

The sums of standard scores were used to derive composite scores. For example, the sum of the Listening Comprehension (LC) and Oral Expression (OE) standard scores creates the Oral Language composite score. Using the standard scores instead of the raw scores provides a more equally weighted scale in the composites.

Because the sums of the standard scores were found to be normal instead of skewed, deriving the composite scores was straightforward. Different ages are accounted for in the initial conversion to standard scores, so when calculating composite scores, it isn’t necessary to have different conversions by age.

Test-Age & Test-Grade Equivalent Scores

The test-age equivalent score is the age in years and months when a raw score or an ability score is the same as the average score. The test-grade equivalent score is the grade placement in grade and tenths of a school year when the raw score or ability score is the same as the average score.

The test-age equivalent scores were developed using the age-based norms for each scale while the test-grade equivalent scores were generated using the grade-based norms for each scale. These equivalent scores were determined by linking the raw score or ability score corresponding to a standard score of 100 for each age or grade group to the midpoint for the age or grade.

When plotted, the raw scores and ability scores created curves used to determine the age and grade equivalent scores for each raw score or ability score.

Development of Standard Scores

The development of standard scores for each scale uses both age-based and grade-based norms, deriving linear standard scores from raw scores and standard deviations. If norm group scores were skewed, normalized scores were calculated from percentile ranks.

Because the OWLS-II evaluates individuals from a very early age into full maturity, it is likely that the distributions will be skewed. Statistics smoothing can be applied to estimate standard deviations and reduce the fluctuation of scores.

The smoothing curves all conform to simple growth curve expectations and using a similar process to the one used in the first OWLS, consistent data points can be established along the developmental curve. The final scores show good measurement.

The accurate development of standard scores means that the scores are reliable for showing normal growth from year to year and identifying anomalies in individuals tested where clinicians can come to logical conclusions and make focused decisions.

For more information on the OWLS-II, visit WPS Publish online.

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