*4.1. Feasibility and Floor Effects*

The NEPSY-II Theory of Mind and SRS-2 both met a priori feasibility criteria and over 85% of participants obtained scores on these measures. Although feasibility was adequate for these measures, percentile ranks were at the floor for the NEPSY-II Theory of Mind. Therefore, we recommend raw scores for use in future work utilizing this measure. Despite relative challenges with theory of mind in DS [14,15], it is encouraging that raw scores were able to capture a range of scores on this measure; however, percentile rank floor effects show that this measure does not discriminate performance between subjects in the sample using published norms. Further, there were minimal differences between raw scores and T-scores on the SRS-2, and the use of T-scores is appropriate for this measure of social behavior. High feasibility of the SRS-2 reinforces the suitability of this tool for the measurement of social behavior in individuals with DS [5,19]. Feasibility was below a priori criterion for the NEPSY-II Affect Recognition and floor effects were observed for both raw and standard scores and most problematic for standard scores. Low feasibility and standard scores on this measure may be, in part, due to difficulties individuals with DS have with recognizing emotional expressions in others [16,17]. Difficulty understanding the task was the greatest reason for noncompletion and assessments of affect recognition with simpler instructions and task demands may be needed for this population. Recommendations for future use of the NEPSY-II Affect Recognition in DS are provided in the discussion of low feasibility measures below.
