# Validation of Smartphone Sway Analysis for Fall Prevention
## 1 Introduction  
Falls among the elderly lead to a serious injury almost 50% of the time [1]. Since falls are the leading cause of death among the elderly, the creation of a method and system of analysis, as well as a monitoring device that will help to assess the risk of falling more conveniently, will be beneficial in helping to diminish the risk of falls. Such a method would need to be able to consider factors of sway that have been identified as major risks. Abnormal sway exhibited by patients were most associated with falling [2, 3]. Historically, a number of physical performance tests and self-report items were used to assess balance in the elderly [4]. Developments in force plate analysis lead to the development of the commercial product \"BTracksS (Balance Tracking Systems, Inc., CA, USA [[http://balancetrackingsystems.com/](http://balancetrackingsystems.com/)]([http://balancetrackingsystems.com/](http://balancetrackingsystems.com/)), accessed on 9 November 2021)\" which became an acceptable clinical tool for postural sway analysis. This tool is based on a force plate [5] which is of the accepted standard for use in medical settings. It is a reliable and accurate device that measures the time-dependent location of the center of pressure (COP) of a subject in order to determine the risk of their fall via examination of the subject's balance. Alternative methods use accelerometers attached to the lower back and a full-body-worn sensor [6, 7, 8]. These accomplish much of the same thing, but allow the measurement of full body kinematics. However, it is difficult to rely on a non-portable method of data collection that requires the patient to travel to a hospital. The mobile option is now viable since more people than ever have smartphones capable of running balance applications in an accurate and meaningful manner [9, 10]. Recent studies have compared commercially available devices--force plate-based versus accelerometer- and gyroscopic data-based--to quantify postural stability [11]. Validity of the sway assessment using a force plate-based system and the industry gold standard Sensory Organization Test (SOT) and Head Shake SOT (HS-SOT) were recently studied, mainly to overcome the high cost of the SOT andHS-SOT systems [12]. Similar smartphone-based applications were used to study frailty after cardiac surgery outcomes [13]. A study to assess sway using a special inertial sensor showed significant differences in the sway characteristics between older non-fallers and fallers [14].  
Today, any smartphone has a built-in accelerometer that may be used to evaluate the sway of the patient. A smartphone device software was developed here to record the sway of the subject and send this information to the investigator. This was completed through the acquisition of the angular deviation of the phone attached to the subject's tibia. At the same time, the corresponding data was acquired from the force plate that provided a temporal record of the center of pressure changes caused by the sway. The primary aim was to determine if the sway variables calculated from these two approaches correlate. A high positive correlation would demonstrate the high validity of the proposed instrument to measure the required characteristics. A positive answer to this question would allow the data from the smartphone application to be used for the analysis of the sway characteristics of a subject instead of using a less portable force plate. This would also remove the need for the subject to come to a doctor's office for the data acquisition, and would allow them to carry it out in his or her home. The results of this study would allow the use of a conventional smart phone with the developed application to be used for the monitoring and prediction of falls in the elderly population.