Establishing Content Validity Evidence of the Pittsburgh Impairment Testing Tool (PITT) for Adults With Spina Bifida

Background: Current scales to measure motor impairment in adults with spina bifida (SB) are limited by their complexity, variable interpretation (i.e., subjectively defined impairment levels), or inclusion of muscles groups that are not always practical to test in a clinical setting. Objectives: A novel motor impairment tool for adults with SB was evaluated for content validity. The tool uses findings from the manual muscle testing of hip flexion and knee extension to categorize individuals into four motor impairment groups. Methods: Expert feedback was obtained on the tool, and content validity was measured using Lawshe’s content validity ratio (CVR) with critical values recommended by Ayre and Scally. Data from phase 1 and phase 2 were used to revise the survey and calculate the CVR of the tool, respectively (benchmark: CVR ≥ 0.636). Results: Of the 26 experts recruited, 17 received the survey and 15 participated in either phase 1 (n = 6) or 2 (n = 11). The CVR values for each impairment group were as follows: intact strength (0.95), thoracic strength (0.90), hip flexor dominant strength (0.89), and knee extensor dominant strength (0.82). The CVR of the tool overall was 0.89. Qualitative expert feedback revealed common barriers to manual muscle testing and suggestions for improving the tool. However, experts also noted the value in preserving the simplicity of the tool. Conclusion: The high content validity, coupled with expert feedback, suggests the tool may give clinicians and researchers a practical method of classifying an individual’s extent of motor impairment.