Measurement Error in Functional Balance and Mobility Tests for People With Stroke: What Are the Sources of Error and What Is the Best Way to Minimize Error?

Abstract

Objective. To assess the degree and source of measurement error in functional balance and mobility tests for people with stroke, and to identify the most effective method of data collection to minimize error. Design. To assess the degree and source of error, the total, systematic, and random error were calculated for within-session, test-retest, and interrater testing. To identify the most effective method of data collection, the total error was calculated for 4 data collection methods: 1 familiarization trial, then scoring a 2nd trial; 2 familiarization trials, then scoring a 3rd trial; averaging 2 trials, then averaging 3 trials. Setting. Stroke services in National Health Service hospitals. Patients. Thirty-five people with a poststroke hemiplegia. Interventions. None. Main Outcome Measures. Five tests provided interval-level data: arm raise (sitting and standing), weight shift, tap, and step-up. Four tests provided ratio-level data: forward reach (sitting and standing) and 5-m timed walk (with and without an aid). Results. Total measurement error ranged from zero for the step-up test to 55% for within-session error for the 5-m walk without an aid. Ratio data tests showed somewhat greater error than interval data tests (5%-55% vs. 0%-46%). A within-session practice effect for the standing forward reach, 5-m walk (with and without an aid), and weight shift tests was found. For the other tests, random error was greater than the systematic error. Interrater testing had the least error. For most tests, the average of 2 trials produced the least measurement error. For the 5-m walk, the mean obtained from 2 or 3 trials was equally effective. For the step-up test, the mean of 3 trials was slightly more effective. The overall error from all 3 sources was 3 lifts for sitting arm raise, 11 cm for sitting forward reach, 3 lifts for the standing arm raise, 7.5 cm for standing forward reach, 4.5 s for walking with an aid, 3 shifts on the weight shift test, 1.1 s for walking without an aid, 2 taps, and 1 step up. Conclusion. The tests using interval data showed less error than ratio-data tests and may be preferable measurement tools. Taking an average of 2 trials was the most accurate data collection method.