Allowing for asymmetric distributions when comparing auditory processing test percentage scores with normative data

BACKGROUND: Raw percentage scores can be transformed to age-specific Z scores, despite the asymmetric distribution of normative data using a process that is applicable to any percentage (or proportion)-based result.

PURPOSE: Normative values are generated for the commonly used dichotic digit and frequency pattern behavioral tests of auditory processing.

STUDY SAMPLE: A total of 180 normal-hearing children aged 7 yr 0 mo to 12 yr 2 mo took part in this study.

RESEARCH DESIGN: A transformation and regression method is incorporated that allows for the asymmetric distribution of normative results and the development of the response across the 7-12-yr-age range.

DATA COLLECTION AND ANALYSIS: Percentage correct scores were determined for each ear in the dichotic digit and frequency pattern tests, delivered at 50 dB HL. The scores were arcsine transformed, then regressed against using an exponential equation, providing an age specific estimated mean score. The residual error of the regression was then used to estimate age specific variance.

RESULTS AND CONCLUSIONS: The ability to express results along an age continuum (while accounting for the asymmetric distribution and significant developmental influences) as a standard unit across all ages enables a simplified expression of performance ability on a task.