Linking Outcomes from Peabody Picture Vocabulary Test Forms using Item Response Models

Paper Title:
Linking Outcomes from Peabody Picture Vocabulary Test Forms using Item Response Models
Journal Link:
http://jslhr.asha.org/cgi/content/abstract/55/3/754
Abstract:
Purpose: The present work describes how vocabulary ability as assessed by three different forms of the Peabody Picture Vocabulary Test (PPVT) can be placed on a common latent metric through item response theory (IRT) modeling, by which valid comparisons of ability between samples or over time can then be made. Method: Responses from 2,625 cases in a longitudinal study of 697 persons for 459 unique PPVT items (175 items from PPVT-R Form M, 201 items from PPVT-3 Form A, and 83 items from PPVT-3 Form B) were analyzed using a two-parameter logistic IRT model.

Results: The test forms each covered approximately ±3 standard deviations of vocabulary ability with high reliability. Some differences between item sets in item difficulty and discrimination were found between the PPVT-3 Forms A and B.

Conclusions: Comparable estimates of vocabulary ability obtained from different test forms can be created via IRT modeling. The authors have also written a freely available SAS program that uses the obtained item parameters to provide IRT ability estimates given item responses to any of the three forms. This scoring resource will allow others with existing PPVT data to benefit from this work as well

Reference:
Hoffman, L., Templin, J., & Rice, M. (2012). Linking outcomes from Peabody Picture Vocabulary Test forms using item response models. Journal of Speech, Language, and Hearing Research, 55, 754-763.
Additional Online Content:
SAS Program for MCMC Scoring of PPVT Item Data