What is the average root mean square error (ARMS)?

The ARMS can be a confusing term to describe pulse oximeter performance, but it is the most common metric used and is required by regulatory bodies. ARMS stands for accuracy root mean square (also known as the average root mean square error or root mean square deviation). It tells you, on average, how close the device’s readings are to your true blood oxygen levels, based on tests in healthy adults in controlled laboratory studies.

The FDA recommends an acceptable limit of ARMS ≤3% for transmittance devices and ARMS ≤3.5% for reflectance devices. It’s helpful to understand that a lower ARMS means the device readings are more accurate and precise. For example, with an ARMS of 2%, the device’s readings would typically be within approximately 2-4% of the true oxygen level. So, if your true oxygen saturation is 94%, then the pulse oximeter reading may be between 90% and 98%.

It is important to recognize that even a small difference in ARMS between devices can reflect a large difference in their performance. 

References: FDA Guidelines; Clinical Application of ARMS in Pulse Oximetry – Clinimark June 2021; Brandmaier et al, Elife 2018

Keywords: bias, standard deviation, Arms, ARMS