Abstract
Background: Attention is a basic neurocognitive function which is a prerequisite for performance on more complex cognitive tasks. The Ruff 2 & 7 test is a well-known measure of attention with a well-supported theoretical and empirical underpinnings. Objective: The Ruff 2 & 7 test, has not been subjected to rigorous item response theory analysis yet. The purpose of this research was to examine the fit of the Ruff 2 & 7 test to the Rasch Poisson Counts Model (RPCM). Methods: Responses of 138 nonclinical subjects to the Ruff 2 & 7 test were analyzed with the RPCM measurement model using ‘lme4’ package in R. The fit of the individual items (blocks) and the overall test to the model were examined. Results: Findings showed that three out of seven scoring techniques fit the Rasch model. The scoring techniques which fitted the model were total number of characters cancelled, total number of characters correctly cancelled, and total number of characters correctly cancelled minus errors of commission. Conclusion: Three of the scoring techniques fit the RPCM which support the internal validity of the test when these scoring procedures were employed. Therefore, the Ruff 2 & 7 test is psychometrically uni-dimensional when these three scores are computed.