Calculation of the 95% Predicted Ellipse Area in R from center of pressure (COP) measurements by means of posturography, following the code as published by Dr. P Schubert and Dr. M. Kirschner. The COP is the resultant of ground reaction forces and is frequently depicted as medio-lateral and anterior-posterior movements, often measured using a force plate, e.g. AMTI, Kistler, Wii Balance Board. A 95% Predicted Ellipse Area may be used to evaluate COP scatter and therefore help to quantify postural sway while maintaining a certain position.
This repository is a fairly simple and straightforward one. It contains a single R file with the code to create a 95% Predicted Ellipse Area, as described by dr. P. Schubert and dr. M. Kirchner in 2014 in the paper Ellipse area calculations and their applicability in posturography. as published in Gait & Posture, 2014, 39, 1: page 558-522.
The R-script is merely a 'translation' of the MATLAB code supplied with the appendix of the article, therefore all credits belong to the original authors as mentioned before.
The script uses two packages: PEIP and ggplot2 which can be found here and here on CRAN respectively and need to be installed before using the function.
The script contains the function pea which takes three arguments: a vector copx which denotes the movement of the COP on the medio-lateral axis, a vector copy for the movement of the COP on the anterior-posterior axis and probability, a single value between 0 and 1.00 to indicate the probability ellipse, which defaults at 95%.
The function pea returns a list with four arguments, which are equal to the results of the original Matlab script. These include: $areawhich contains the area, $eigenvectors calculated eigenvectors of the data, $eigenvalues eigenvalues of the copx and copy data and $plot using the ggplot2 package.
Feel free to send me an e-mail at t.vredeveld (at) hva (dot) nl, make a pull-request or create an issue.