The use of fractal dimension methods in clinical epidemiology: an application for postural assessment

<p><strong>Background:</strong> this study considers the analysis of postural sway by comparing the use of a fractal dimension outcome (DBOX) with the usual sway ellipse area (SEA), calculated by the least squares method. Both the response variables come from centre of pressure (COP) dynamics detected by means of a force platform.</p><p><strong>Methods:</strong> recent literature regarding postural stability assessment in subjects with muscularskeletal disorders, or neuromuscular diseases affecting their motor skills, has suggested, both for practical and theoretical reasons, the use of some fractal dimension as a good outcome measurement for overall postural status. A sample group of 24 male subjects was recruited. The postural stabilogram was recorded both with eyes open (EO) and eyes closed (EC) while standing upright. A matched-pair comparison of the sway ellipse area with the COP dynamics box counting dimension was performed. A ROC analysis of the outcome variables was performed. Then, a ROC comparison of the tests, using the area under the curve (AUC) index, was conducted.</p><p><strong>Results:</strong> the comparison of paired groups showed a statistically significant difference between EO and EC status, according to the sway ellipse area and the fractal dimension (p&lt;0.05). The ROC analysis, describing the test performance in terms of AUC difference, was statistically significant (p&lt;0.05). The comparison of the AUCs showed an overall superior performance of the DBOX with respect to SEA (p&lt;0.05).</p><p><strong>Conclusions:</strong> this study showed a statistically significant better overall performance of DBOX with respect to SEA, suggesting possible improvements of clinical practice, as well as theoretical insights into the response patterns.