Rasch analysis of the Bruininks-Oseretsky Test of Motor Proficiency-Second Edition in intellectual disabilities.

The Bruininks-Oseretsky Test of Motor Proficiency-Second Edition (BOT-2) is widely used to assess motor skills for both clinical and research purposes; however, its validity has not been adequately assessed in intellectual disabilities (ID). This study used partial credit Rasch model to examine the measurement properties of the BOT-2 among 446 children and adolescents with ID aged 4-18 years. Seventeen items were identified as problematic in the Rasch modeling. After removal of these items, the appropriateness of the response categories was examined in the 36 remaining items. Where the item response categories failed to express an increasing level of the trait (disordered thresholds), collapsing adjacent categories was performed to address this issue. After rescoring most items, items in each composite of the revised BOT-2 showed good fit to the Rasch model and demonstrated excellent reliability (range 0.90-0.97). No differential item functioning was detected with respect to age and gender. The ability of the revised composites to differentiate between mild versus moderate to severe ID was better than those of the original BOT-2. Items from the manual coordination and strength and agility composites were well targeted to the sample, whereas items from fine manual control and body coordination composites were mostly targeted at the lower levels of ability in these domains. Items of higher difficulty may be supplemented to increase the range of ability levels of the people to whom these two composites can be applied with precision.