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1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

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likelihood estimation was used in Stata 9.1 statistical software to estimate these mo<strong>de</strong>ls. The<br />

mo<strong>de</strong>l was exten<strong>de</strong>d to analyse data from all points in the gait cycle simultaneously by<br />

including fixed effects for percentage point of the gait cycle.<br />

Results<br />

Inter-trial, inter-session and total error estimates (incorporating both trial and session<br />

variability) varied across gait parameters and assessors. As an example, Figure 1 illustrates<br />

differences in total pelvic tilt error from the 6 assessors. The magnitu<strong>de</strong> of error in key gait<br />

parameters appeared related to experience, with the most experienced (ME) assessors generally<br />

recording lower errors than less experienced (LE) assessors. This was particularly evi<strong>de</strong>nt in<br />

key parameters sensitive to marker misplacement such as pelvic tilt (ME 2.5<strong>de</strong>g),<br />

hip rotation (ME 5 <strong>de</strong>g) and foot progression (ME 2 <strong>de</strong>g).<br />

Standard <strong>de</strong>viation (<strong>de</strong>g)<br />

Total variability<br />

0 1 2 3 0 1 2 3<br />

Pelvic Tilt: Total of session and trial variability<br />

0 50 100 0 50<br />

% of gait cycle<br />

100 0 50 100<br />

Figure 1: Errors in pelvic tilt for a single subject measured by 6 assessors. Each<br />

graph represents the total of session and trial variability from a single assessor<br />

Discussion<br />

Quantification of the error sources associated with 3D analysis has varied applications.<br />

Knowledge of a single assessor’s typical inter-session error may be relevant in laboratories<br />

with a single staff assessor, or where a <strong>de</strong>signated assessor routinely repeats 3DGA on patients<br />

returning for evaluations. Determination of inter-assessor error within a laboratory will assist<br />

in <strong>de</strong>fining gait parameters which reflect systematic assessor <strong>de</strong>viations in marker placement<br />

protocols. Evaluation of inter-assessor error within and across laboratories is relevant for<br />

multi-centre collaborative research and in construction of shared gait databases. Quantitative<br />

feedback of individual and within-laboratory assessor reliability offers opportunities to more<br />

specifically direct quality assurance activities including biomechanical mo<strong>de</strong>l review and<br />

marker placement training and practice. This method may also permit a closer evaluation of the<br />

relationships between assessor experience, training and error profiles. This report uses data<br />

from a single unimpaired subject to illustrate the potential application of this approach. The<br />

techniques are equally applicable to multiple subjects from relevant clinical populations with<br />

gait pathology.<br />

References<br />

[1] Gorton G et al. (2002) Gait and Posture,16 (suppl 1): p. S65-66.<br />

[2] Schwartz MH et al. (2004), Gait and Posture, 20, 296-203.<br />

[3] Dunn G (2004) Statistical Evaluation of Measurement Errors.<br />

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