Through the process of research investigations, it was discovered that absolute scores outperform normative scores. Because norm-referenced scores do not provide information regarding skill gain, stability, or loss, they are unsuitable for natural history research or clinical trials. The typical metric in this type of research has been age-equivalent (AE) scores. While physicians and parents are familiar with and can interpret AEs, they are imprecise due to a lack of standard deviations, standard errors of measurement, and uniform intervals between scores.
Indicated for measuring change in natural history research and clinical trials for patients who perform poorly, flatly, or decline on outcome measures, Growth Scale Values (GSVs) provide an accurate estimate of within-person change. GSVs avoid erroneous AEs, are not restricted by age, and can be utilized for out-of-level testing. Additionally, GSVs have interval features, and each GSV value has a known standard deviation (SEM).