TABLE 1
Initial features considered for testing in the model
| Factors | Comment or explanation |
| Fourier transform of Respeck signal | Normalised as  |
| Mean, median and standard deviation of individual breathing rates | Extreme values are less likely to be reliable A smaller standard deviation reflects more regular breathing |
| Maximum–minimum rate | A large range of rates within the sampling window would be less trustworthy |
| Mean and median of differences | Mean and median of frequency differences between one breath and the next within the window |
| Standard deviation of axis acceleration values | A measure of large changes in axis signal, often associated with posture changes |
| Standard deviation, median and skew of activity levels | Activity level is computed as the length of the vector differences using the x, y and z coordinates |
| Standard deviation of Respeck signal | A large standard deviation indicates probable posture change |
| Number of valid breaths | A small number of detected breaths suggests the signal is unreliable |
| Standard deviation of Respeck amplitude peaks | Greater variation in the size of breaths in a window suggests unstable breathing |
| Mean and median of peak differences | Large differences between breath amplitudes suggest unstable breathing |
| Mean and median of peak intervals | Times between successive peaks in the window should be similar |
These are derived from the waveform of the Respeck signal, the accelerometer signals and the breath timing measurements.