Original research| Volume 99, ISSUE 8, P1491-1498.e1, August 2018

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Validation of the Narrowing Beam Walking Test in Lower Limb Prosthesis Users

Published:April 10, 2018DOI:



      To evaluate the content, construct, and discriminant validity of the Narrowing Beam Walking Test (NBWT), a performance-based balance test for lower limb prosthesis users.


      Cross-sectional study.


      Research laboratory and prosthetics clinic.


      Unilateral transtibial and transfemoral prosthesis users (N=40).


      Not applicable.

      Main Outcome Measures

      Content validity was examined by quantifying the percentage of participants receiving maximum or minimum scores (ie, ceiling and floor effects). Convergent construct validity was examined using correlations between participants’ NBWT scores and scores or times on existing clinical balance tests regularly administered to lower limb prosthesis users. Known-groups construct validity was examined by comparing NBWT scores between groups of participants with different fall histories, amputation levels, amputation etiologies, and functional levels. Discriminant validity was evaluated by analyzing the area under each test’s receiver operating characteristic (ROC) curve.


      No minimum or maximum scores were recorded on the NBWT. NBWT scores demonstrated strong correlations (ρ=.70‒.85) with scores/times on performance-based balance tests (timed Up and Go test, Four Square Step Test, and Berg Balance Scale) and a moderate correlation (ρ=.49) with the self-report Activities-specific Balance Confidence scale. NBWT performance was significantly lower among participants with a history of falls (P=.003), transfemoral amputation (P=.011), and a lower mobility level (P<.001). The NBWT also had the largest area under the ROC curve (.81) and was the only test to exhibit an area that was statistically significantly >.50 (ie, chance).


      The results provide strong evidence of content, construct, and discriminant validity for the NBWT as a performance-based test of balance ability. The evidence supports its use to assess balance impairments and fall risk in unilateral transtibial and transfemoral prosthesis users.


      List of abbreviations:

      ABC (Activities-specific Balance Confidence), BBS (Berg Balance Scale), CI (confidence interval), FSST (Four Square Step Test), IQR (interquartile range), LLP (lower limb prosthesis), ROC (receiver operating characteristic), TUG (timed Up and Go)
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