A Simple Post Hoc Transformation that Improves the Metric Properties of the BBB Scale for Rats with Moderate to Severe Spinal Cord Injury

Abstract

The Basso, Beattie, Bresnahan (BBB) open field locomotor scale is a popular measure of functional recovery following spinal cord injury (SCI). To examine the metric properties of the scale, we performed detailed analyses of BBB scores from 643 rats with moderate and severe SCI (12.5, 25, or 50 mm MASCIS) from two different laboratories. The analyses revealed that the BBB scale is ordinal in the most frequently used portion of the scale. Higher scores (14 and greater) were not frequently assigned in the dataset as animals with mild injuries were not sampled, making the ordinal nature of the upper end of the scale difficult to assess. The rare scores assigned in this range disproportionately increased variance. Under these conditions collapsing scores above 14 into one category increased effect size. Analysis of the lower region of the scale revealed that some scores (2 and 3) were rarely assigned, implying a discontinuity in the scale. The discontinuous nature of the lower portion of the scale presents a problem for both parametric and nonparametric statistical analyses. Pooling scores 2/3/4 eliminated the gap, enhancing the metric properties of the scale. Under the injury conditions evaluated, the transformation helped assure that the data were continuous and ordered. Further, interval durations were comparable across the entire range of the transformed scale, allowing application of parametric statistical techniques. The transformation should be applied in a post hoc fashion to reduce variability and increase power in cases where few scores fall in upper portion of the scale.

The Irvine, Beatties, and Bresnahan (IBB) Forelimb Recovery Scale: An Assessment of Reliability and Validity

“…Categories were loosely arranged to reflect the sequence of recovery, and scores were assigned (0, 1, 2) to reflect the rank-ordered attributes. Initial scaling involved summation of these ranked features and then the resulting 55-point scale was subjected to evaluation of the metric properties such as score frequency distribution, ordinality, discontinuities, and interval properties (22). This analysis revealed that certain features did not progress in an ordered sequence and further reanalysis revealed problems with reliability and sensitivity that increased measurement error and reduced ordinality.…”

“…The usefulness and metric properties of motor outcome scales are not always tested or considered in the SCI literature. But in response to suggestions made as more and more laboratories adopted the BBB and more data became available, this scale was modified in light of a growing body of data that suggested the metric properties were not optimized (22). A similar approach has been taken in the construction of scales for walking in human SCI patients (23).…”

Dietary Omega-3 Polyunsaturated Fatty Acids Improve the Neurolipidome and Restore the DHA Status while Promoting Functional Recovery after Experimental Spinal Cord Injury

“…22,28 This transformation produces a continuous distribution by pooling together BBB scores from 2-4 and 14-21 and thus avoids potentially suspect measures…”

Plasticity of connections underlying locomotor recovery after central and/or peripheral lesions in the adult mammals

“…However, it is based on qualitative assessment and its linear scale does not account for the nonlinearity of locomotor recovery. Moreover, the lowest and highest scores are not necessarily used (the worst and the best performances), which may distort statistics (see, however, the correction suggested by the originators of this scale; Ferguson et al 2004).…”