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Validity of balance measures in cerebellar ataxia: A prospective study with 12-month follow-up
Stanley J Winser1,2, Anne Y Y Chan3,4, Raymond Chung1
1Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong Kong.
Introduction:
Balance deficits are common in cerebellar ataxia. Determining which balance outcome measures are psychometrically strong for this population remains an unmet need.
Objective:
To evaluate the validity and responsiveness of two clinic-based balance measures (Berg Balance Scale [BBS] and balance sub-component of the Scale for the Assessment and Rating of Ataxia [SARA-bal]) and two laboratory-based balance measures (Sensory Organization Test [SOT] and Limits of Stability [LOS]) in cerebellar ataxia.
Design:
Prospective cohort study.
Setting:
Institutional study assessing 40 participants with cerebellar ataxia at baseline, and 6 and 12 months.
Main Outcome Measures:
Balance was assessed using the BBS, SARA-bal, SOT, and LOS; disease severity was assessed using the SARA; and Patients' Global Impression of Change (PGIC) was used to estimate responsiveness to disease progress at 6 and 12 months.
Results:
BBS and SARA-bal (Spearman's correlation coefficient, ρS = -0.89, p < .01) demonstrated strong criterion validity. Convergent validity was moderate to high (ρS range: -0.75 to 0.92) and external validity was low (ρS range: -0.75 to 0.11). Composite SOT scores (SOT-COM; ρS = 0.29, p < .01) and maximal excursion (MXE-LOS) in the forward (F) and right (R) directions of the LOS (ρS = 0.18, p < .01) demonstrated moderate to low criterion and convergent validity. The area under the receiver-operating characteristic curve (AUCROC ) and its effect size (standard response mean [SRM]) for categorizing "stable" and "worsened" patients at 6 and 12 months were satisfactory for the BBS (AUCROC : 0.75; SRM-Stable: 1.06; SRM-Worsened: 1.16), SARA-bal (AUCROC : 0.76; SRM-Stable: 0.86; SRM-Worsened: 0.85), and MXE-LOS(R) (AUCROC : 0.29; SRM-Stable: 0.41; SRM-Worsened: 1.39).
Conclusion:
BBS and SARA-bal have moderate to strong criterion and convergent validity and adequate responsiveness to balance changes. Both laboratory-based measures (SOT and LOS) demonstrated a high floor effect. The SOT-COM and MXE-LOS(R) demonstrated moderate to low criterion validity, with only the MXE-LOS(R) displaying adequate responsiveness to balance changes after 6 and 12 months.
