The term “validity” is typically used in the context of a psychometric instrument (anxiety scale, etc.). However, it is not a term that is used in describing the accuracy of physiological instruments. In the case of HRV (Heart Rate Variability) Coherence, which is what the emWave’s measure and assess, the accuracy of the measurement of the IBI (inter-beat interval) is solely determined by the sample rate. The sample rate of the emWave is 250 Hz.