The aim of this brief technical note was to focus on a widely used method for evaluating the statokinesigram: the confidence ellipse. We pointed out that several authors misinterpret the meaning of confidence ellipse, which is actually well defined in statistics. Most of the researchers use the parameters of the Time Domain (calculated by the Discrete Fourier Trasform) and those of the Areas Domain of the sway. The Area of the circle includes almost 95% of the sway path, and it is called in a incorrectly: Confidence Circle Area. Ellipse Area includes also almost 95% of all the points of the sway, incorrectly named Confidence Ellipse Area, and it can be associated to the stabilogram. In this case it is possible to assume some more informations such as: the mean direction of all the sway path and the ellipse shape. Considering Area it is possible to calculate also: the mean distance from the Centre of Gravity (CG), the mean distance on the antero-posterior axis, the mean distance on the medio-lateral axis. Anyway we illustrated some limitations when using confidence ellipse in evaluating statokinesigram. Finally we suggested substituting confidence ellipse with the standard ellipse. In fact it is possible to use different parameters to measure the common postural tasks and the sway resulted from the subjects’ strategies.
The misuse of the confidence ellipse in evaluating statokinesigram
ROCCHI, MARCO BRUNO LUIGI;SISTI, DAVIDE;DITROILO, MASSIMILIANO;CALAVALLE, ANNA RITA;
2005
Abstract
The aim of this brief technical note was to focus on a widely used method for evaluating the statokinesigram: the confidence ellipse. We pointed out that several authors misinterpret the meaning of confidence ellipse, which is actually well defined in statistics. Most of the researchers use the parameters of the Time Domain (calculated by the Discrete Fourier Trasform) and those of the Areas Domain of the sway. The Area of the circle includes almost 95% of the sway path, and it is called in a incorrectly: Confidence Circle Area. Ellipse Area includes also almost 95% of all the points of the sway, incorrectly named Confidence Ellipse Area, and it can be associated to the stabilogram. In this case it is possible to assume some more informations such as: the mean direction of all the sway path and the ellipse shape. Considering Area it is possible to calculate also: the mean distance from the Centre of Gravity (CG), the mean distance on the antero-posterior axis, the mean distance on the medio-lateral axis. Anyway we illustrated some limitations when using confidence ellipse in evaluating statokinesigram. Finally we suggested substituting confidence ellipse with the standard ellipse. In fact it is possible to use different parameters to measure the common postural tasks and the sway resulted from the subjects’ strategies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
