Preliminary evidence of equivalence of alternate forms of the ImPACT.

The ImPACT (Immediate Postconcussion Assessment and Cognitive Testing) is a computerized neurocognitive test used to assist in the management of sport concussion management. A number of studies have documented the reliability and sensitivity of the ImPACT, but no studies have examined the equivalence of the ImPACT's alternate forms. The objective of our study was to determine the equivalence of the ImPACT's five alternate forms. Participants were administered alternate forms of ImPACT based on clinically relevant time frame derived from an extensive sports concussion database. Participants completed a baseline assessment followed by various combinations of the remaining alternate forms at 45 and 50 days. Inferential Confidence Intervals were calculated for each composite score for all alternate forms. We found non-equivalence between ImPACT form 1 and forms 2, 3, and 4 on the Verbal Memory and between forms 2 and 4. ImPACT forms 1 and 3 were not equivalent on the Visual Memory Composite. Finally, ImPACT forms 3 and 4 were not equivalent on the Visual Motor Speed and Reaction Time Composites. Alternate form equivalence is necessary to minimize measurement error and optimize clinical decision making. Clinicians using the ImPACT should consider non-equivalence of some forms on certain Composites when interpreting ImPACT following sports concussion.