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 |

Maximumâ€“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.