Title:
Pedometer variance in adults with Down syndrome during free walking: a generalizability study.

Abstract:
Pedometers are a common instrument used to measure walking activity, yet reliability evidence in disability populations, particularly Down syndrome (DS), has received little attention. There may be systematic and random sources of error that could influence reliability under natural walking conditions. The purpose of this study was to examine the sources of variance and estimate reliability coefficients of spring-levered (SL) and piezoelectric (PZ) pedometers for adults with DS during a free-walking bout.
Seventeen adults with DS and 23 adults without a disability walked continuously for a 20-minute period wearing 2 types of pedometers, SL and PZ. Step counts were analyzed using Generalizability theory to partition and quantify variance components and calculate reliability coefficients.
The largest variance component was due to individual participant differences. Adults with DS demonstrated greater intraindividual variability, but also had relatively low proportions of residual variance, or unexplained error. The SL pedometer showed problems with interunit variance while the PZ pedometer demonstrated little systematic error. Reliability coefficients were consistently higher for the PZ pedometer.
This study found minimal systematic error and moderate reliability evidence for the PZ pedometer. This type of pedometer may be used in future research for adults with DS.